============================================================

    U.S. Robotics Courier/PC High Speed Modems

============================================================


+----------------------------------------------------------+
|                                                          |
|   HOW TO USE THIS MANUAL                                 |
|                                                          |
+----------------------------------------------------------+

This manual contains operating instructions for Courier V.32
terbo/PC,  and Courier HST Dual Standard/PC modems.  They
are designed for installation in any 100% IBM PC-compatible
computer.

These modems have many similar features except for the
signaling they use to connect with remote modems at high
speeds:  V.32/V.32 terbo or HST.  Courier HST Dual
Standard/PC modems use either type of signaling, depending
on the type of remote modem.  In addition, the V.32 terbo
can connect at rates of up to 21.6K bps, while HST Dual
Standards in HST mode can connect at rates of up to 16.8K
bps.

If you've purchased a Courier V.32 terbo/PC modem, disregard
the instructions in this manual concerning HST operations.
Below is a brief description of the manual's contents.

#    Chapter 1--Operating and compatibility features
#    Chapter 2--Installation and testing
#    Chapter 3--Data mode commands
#    Chapter 4--Fax mode and Call Selection
#    Chapter 5--Queries and Help commands to display current
     settings, operational summaries, and other data

The Appendixes in Part II cover the following subjects.

#    Background information on error control, throughput and
     flow control
#    Summaries and tables
#    Dial Security operations
#    Troubleshooting
#    Additional features such as Dedicated and Leased Line
     operations, HST Cellular operations, and voice/data
     communications
#    Procedures for modem testing
#    Glossary
#    Warranty/Service/Certification information



A NOTE ON COMMUNICATIONS SOFTWARE
------------------------------------------------------------

Many brands of communications software are available, all of
which are based on the modem's AT command set.
Some users prefer their communications software to take
control of the modem, and are more comfortable with a
program that makes the modem almost transparent.   Others
prefer a program that allows them to use the modem's AT
command set sometimes, and their software at other times,
depending on the task at hand.
























































































------------------------------------------------------------
U.S. Robotics, the U.S. Robotics logo and HST are registered
trademarks of U.S. Robotics, Inc.  Courier HST Dual Standard
Fax, Courier V.32 terbo Fax, Total Control, and Adaptive
Speed Leveling (ASL) are trademarks of U.S. Robotics, Inc.
Any trademarks, tradenames, service marks or service names
owned or registered by any other company and used in this
manual are the property of their respective companies.
------------------------------------------------------------
TABLE OF CONTENTS
------------------------------------------------------------
How to Use this Manual                                     1
Table of Contents                                          4
Limited Warranty                                           7
FCC Registration Numbers                                   8
DOC (Canada)                                               8
Connecting to the Telephone Company                        8
Radio and Television Interference                          9
For Canadian Modem Users                                   9

PART I.  INSTALLATION AND OPERATION

Chapter 1--Features and Compatibility
Introduction                                              11
Compatibility                                             14
Fax Standards                                             15

Chapter 2--Set-Up and Testing
Package Components                                        16
Operational Requirements                                  16
Installing the Modem                                      16
Testing the Installation                                  21

Chapter 3--Data Mode Command Summary
Command Set Usage                                         24
Basic Commands                                            26
Dialing/Answering                                         26
Dialing (D)                                               26
Dial Options                                              26
Store Phone Numbers                                       28
Redialing                                                 28
Answer Mode                                               29
Hanging Up (H, +++)                                       31
Setting/Using Defaults (&Fn, &W, Z)                       32
Configuration                                             34
Echo/Speaker (En, Fn, Mn, Ln)                             34
Result Codes (Qn, Vn, Xn)                                 35
Additional Result Codes (&An)                             38
Modulation (Bn)                                           39
Error Control/Data Compression (&Mn, &Kn)                 40
Data Rates (&Bn, &Nn)                                     41
Computer/Modem Signal Controls
     (&Cn, &Dn, &Sn)                                      43
Flow Control (&Hn, &In, &Rn)                              44
S-Registers                                               49
Inquiry and Help                                          49
Testing                                                   49
International Calls (&Gn, &Pn)                            49
Miscellaneous Commands                                    50

Chapter 4--Fax Operations and Call Selection
Fax Operations                                            52
Call Selection                                            54

Chapter 5--Queries and Help Screens 
User Inquiries (In)                                       55
S-Register Query (Sr?)                                    58
Phone Number Query (&Zn?)                                 59
Last-Dialed Number Inquiry (DL?)                          59
Stored Command String Query (&ZC?)                        59
Help Screens                                              59
   Stop/Restart Display                                   59
   Cancel Display                                         59
   Basic Command Set ($)                                  60
   Extended Command Set (&$)                              60
   Dialing (D$)                                           60
   S-Register Functions (S$)                              60
   Percent Commands (%$)                                  60


PART II. REFERENCE

Appendix A--Link Negotiation (Handshaking)
     and Error Control   
Link Negotiation (Handshaking)                            61
HST Mode                                                  61
V.32 terbo Mode                                           63
Dual Standard Handshaking                                 65
Error Control and Throughput                              65
V.42 Handshaking                                          65
MNP Handshaking                                           66
Data Compression                                          66
Flow Control                                              67
Throughput Guidelines                                     67
Achievable Throughput                                     69

Appendix B--Summaries and Tables    
DIP Switch Summary                                        72
Default Settings                                          74
Factory Templates
     &F1 Hardware Flow Control (Default)                  75
     &F2 Software Flow Control                            76
     &F3 HST Cellular Operations                          77
     &F0 No Flow Control                                  78
S-Register Summary                                        80

Appendix C--Dial Security/Remote Access  
Dial Security                                             91
Remote Access                                             98

Appendix D--Troubleshooting                              104

Appendix E--Additional Operations   
Dedicated and Leased Line Operations                     110
HST Cellular Operations                                  112
Voice/Data Communications                                114
Hewlett Packard 3000 Installations                       115

Appendix F--Modem Testing 
Testing with &T                                          116
   Ending a Test--&T0, S18                               116
   Analog Loopback--&T1, &T8                             116
   &T2                                                   118
   Digital Loopback--&T3                                 118
   &T4, &T5                                              119
   Remote Digital Loopback--&T6, &T                      119
Testing with Register S16                                122
   Analog Loopback--S16=1D                               122
   Dial Test--S16=2                                      123
   Test Pattern--S16=4                                   123
   Remote Digital Loopback--S16=8                        124

Appendix G--Glossary                                     126

Appendix H--Technical Specifications                     136




































LIMITED WARRANTY
------------------------------------------------------------

U.S. Robotics, Inc., warrants to the original consumer or
other end user purchaser that this product is free from
defects in materials or workmanship for a period of two
years from the date of purchase.  During the warranty
period, and upon proof of purchase, the product will be
repaired or replaced (with the same or similar model) at our
option, without charge for either parts or labor.  This
warranty shall not apply if the product is modified,
tampered with, misused, or subjected to abnormal working
conditions.

------------------------------------------------------------
REPAIR OR REPLACEMENT AS PROVIDED UNDER THIS WARRANTY IS THE
EXCLUSIVE REMEDY OF THE PURCHASER.  THIS WARRANTY IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING ANY
IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A
PARTICULAR USE OR PURPOSE, AND U.S. ROBOTICS SHALL IN NO
EVENT BE LIABLE TO PURCHASER FOR INDIRECT OR CONSEQUENTIAL
DAMAGES OF ANY KIND OR CHARACTER.
------------------------------------------------------------

Some states do not allow the exclusion or limitation of
incidental or consequential damages or allow limitations on
how long an implied warranty lasts, so the above limitations
or exclusion may not apply to you.  This warranty gives you
specific legal rights.  You may also have other rights which
vary from state to state.

To obtain service under this warranty, contact the U.S.
Robotics Technical Support Department by fax, (708) 982-
5235, by phone, (800) 982-5151, or by mail, 8100 North
McCormick Blvd., Skokie, Illinois, 60076-2999.  Include your
serial number and proof of purchase or have them ready if
you phone.  You will be given a Return Materials
Authorization (RMA) number to help us keep track of your
warranty request.  Once you have received your RMA number,
take or mail the product, postage prepaid, to U.S. Robotics
at the above address.  Include proof of the date of
purchase.  IMPORTANT:  If you ship your unit, pack it
securely, be sure your RMA number is visible on the outside
of the package, and ship it charges prepaid and insured.
Modems without an RMA will not be accepted.

Should you encounter problems in operating this device,
follow the instructions in Appendix D in Part II of this
manual.  The appendix contains solutions to operating
problems as well as procedures to follow if there is an
apparent modem malfunction.



FCC REGISTRATION
------------------------------------------------------------

This device complies with Part 15 of the FCC Rules.
Operation is subject to the following two conditions:
1.   this device may not cause harmful interference;
2.   this device must accept any interference received
     including interference that may cause undesired
     operations.

     FCC68:  CJEUSA-65828-FA-E
     RINGER EQUIVALENCE:  0.4B
     FCC15:  CJE-02236CR

DOC (CANADA)
------------------------------------------------------------

This digital apparatus does not exceed the Class B limits
for radio noise emissions from digital apparatus set out in
the radio interference regulations of the Canadian
Department of Communications.

Le present appareil numerique n'emet pas de bruits radio-
electriques depassant les limites applicables aux appareils
numeriques de la classe B prescrites dans le Reglement sur
le brouillage radioelectrique edicte par le ministere des
Communications du Canada.

UL RECOGNITION/CSA APPROVAL
------------------------------------------------------------

This information technology equipment is UL-recognized and
CSA-approved for the uses described in this manual.

CONNECTING TO THE TELEPHONE COMPANY
------------------------------------------------------------

It is not necessary to notify the telephone company before
installing the modem.  However, the telephone company may
request the telephone number(s) to which the Courier is
connected and the FCC information printed above.

If the telephone company has any questions or raises
problems, ask them to call the Technical Support Department,
U.S. Robotics, Inc., (800) 982-5151.

If the modem is malfunctioning, it may affect the telephone
lines.  In this case, disconnect the modem until the source
of the difficulty is traced.  Do not use the modem on party
or coin telephone lines.




RADIO AND TELEVISION INTERFERENCE
------------------------------------------------------------

This equipment generates and uses radio frequency energy and
if not installed and used properly, in strict accordance
with the  manufacturer's instructions, may cause
interference to radio and  television reception.  Courier
high speed modems have been tested and found to comply with
the limits for a Class B computing device in accordance with
the specifications in Part 15 of FCC rules, which are
designed to provide reasonable protection against such
interference in a residential installation.

However, there is no guarantee that interference will not
occur in a particular installation.  If this device does
cause interference to radio or television reception, which
you can determine by monitoring reception when the computer
is on and off, try to correct the problem with one or more
of the following measures.

#    Reorient the receiving antenna.
#    Relocate the computer with respect to the receiver.
#    Relocate the computer and/or the receiver so that they
     are on separate branch circuits.

If necessary, consult your dealer or an experienced radio/
television technician for additional suggestions.  You may
find the following booklet, prepared by the Federal
Communications Commission, helpful:

     How to Identify and Resolve Radio-TV
          Interference Problems
     Stock No. 004-000-0345-4
     U.S. Government Printing Office
     Washington, DC 20402

In accordance with Part 15 of the FCC rules, any
modification to or tampering with this device that causes
harmful interference to others may be reason for prohibiting
future operation.

FOR CANADIAN MODEM USERS
------------------------------------------------------------

The Canadian Department of Communications (DOC) label
identifies certified equipment.  This certification means
that the equipment meets certain telecommunications network
protective, operational, and safety requirements.  The
department does not guarantee the equipment will operate to
a user's satisfaction.

Before installing this equipment, make sure you are
permitted to connect it to the facilities of the local
telecommunications company.  You must also install the
equipment using an acceptable method of connection.  In some
cases, you may also extend the company's inside wiring for
single line individual service by means of a certified
connector assembly (telephone extension cord).  You should
be aware, however, that compliance with the above conditions
may not prevent degradation of service in some situations.

Repairs to certified equipment should be made by an
authorized Canadian maintenance facility designated by the
supplier.  Any repairs or alterations made by a user to this
equipment, or equipment malfunctions, may give the
telecommunications company cause to request the user to
disconnect the equipment.

For your own protection, make sure that the electrical
ground connections of the power utility, telephone lines,
and internal metallic water pipe system, if present, are
connected together.  This precaution may be particularly
important in rural areas.

CAUTION:  Do not attempt to make such connections yourself;
contact the appropriate electric inspection authority or
electrician.

Courier High Speed Modems Load Number:  5

The Load Number (LN) assigned to each terminal device
denotes the percentage of the total load to be connected to
the telephone loop used by the device, without overloading.
The  termination on a loop may consist of any combination of
devices, subject only to the requirement that the total of
the Load Numbers of all the devices not exceed 100.






















+----------------------------------------------------------+
|                                                          |
|   CHAPTER 1.  FEATURES AND COMPATIBILITY                 |
|                                                          |
+----------------------------------------------------------+

INTRODUCTION
------------------------------------------------------------

Congratulations.  The Courier modem you've purchased repre-
sents powerful, advanced electronic design that offers
exceptional reliability, compatibility and flexibility at
all standard rates up to 19,200 bps or 19.2K bits per second
(bps).  The transmission rate between the computer and
modem, depending on your equipment and software support, can
be as high as 115.2K bps.

The following features and capabilities assure you of
superior reliability and performance.

CONNECTIONS UP TO 21.6K BPS
With our new implementation of V.32 terbo, two Courier
modems with this feature can connect at rates up to 21.6K
bps as well as rates of 19.2K bps and 16.8K bps.  These
rates represent a rate of up to over 30% greater than the
rates of standard ITU-T (formerly CCITT) V.32 bis modems
which are limited to calls of 14.4K bps or lower.

QUICK TRAIN
Courier high speed modems can handshake and start
transmitting in less than 2 seconds, in contrast to typical
training times that range between 9 and 18 seconds.

HIGH SPEED CALLS--ADAPTIVE SPEED LEVELING (ASL)
Like most high speed modems, Courier modems fall back to the
next lower speed, for example, 19.2K, then 16.8K, if poor
line conditions warrant.  In addition, Courier modems detect
improved line conditions and shift upward again to the next
higher speed.  ASL keeps the modems online, always operating
at the highest possible speed, and constantly ensuring data
integrity.

FAX CAPABILITY--COURIER FAX MODEMS
You can use your modem in Class 1, Class 2.0, and Group III
facsimile mode for sending or receiving faxes.

ERROR CONTROL--V.42/MNP
Data integrity is ensured when the modems connect with
remote modems that use the V.42 (LAPM), USR-HST, or MNP
error control protocols.  Error control is available on
calls at 1200 bps and above.

DATA COMPRESSION--V.42 BIS/MNP5
Data compression enables potential throughput of well over
60K bps on 19.2K or 21.6K  bps connections.  Couriers
connecting under V.42 or HST error control use V.42 bis com-
pression.  Couriers connecting under MNP error control use
MNP Level 5 compression.  Sample tables of achievable
throughput of text and other types of files are listed in
Appendix A.

FLOW CONTROL/VARIABLE INTERFACE RATES
Flow control, required under error control, also allows the
local computer interface rate to be set higher than the link
rate, enabling greater efficiency and throughput.  If your
equipment and software support high rates, data can be sent
from the computer to the modem at 115.2K, 57.6K, 38.4K or
19.2K bps, regardless of the link rate.

DIAL SECURITY
With Dial Security, you will be able to prevent unauthorized
access to a system with the use of Autopass, Prompting, and
Dialback.  See Appendix C for more information.

PROGRAMMABLE NONVOLATILE MEMORY
You can tailor your own default settings and store them in
nonvolatile random access memory (NVRAM).  Each time the
Courier is powered on or reset, it operates at the settings
you've specified.

LINK RATE NEGOTIATION
The Courier automatically lowers its link rate to match a
lower rate of a remote modem, in both Originate and Answer
Modes, allowing connections with a wide range of installed
modems.

LINK DIAGNOSTICS
After each call, you can display a Link Diagnostics screen
containing information about the last call, including the
number of data characters transferred, line statistics, the
call's rate and the reason the call was disconnected.

MODEM DIAGNOSTICS
ITU-T V.54 loopback testing with the &T command options, and
earlier Courier Register S16 test options are available.
The modem performs three loopback tests:  analog, digital,
and remote digital.  See Appendix F for information.

INACTIVITY TIMER
You can set the modem to automatically hang up after a
specified number of minutes if there is no activity on the
phone line.

CALL DURATION REPORTING
The modem records the duration of your calls in hours,
minutes, and seconds.  This feature enables you to display
and print an audit of your calling activities.  You can
optionally use the modem clock as a real-time clock.
CALL PROGRESS DETECTION
An optional set of result codes (screen messages) lets you
know when a line is busy, a person rather than a modem has
answered the phone, there is no dial tone, or the distant
phone is ringing.

MODEM SETTINGS DISPLAYS
On command, the modem displays its current settings, a handy
way to check your transmission rate, S-Registers and other
operational controls.  The modem also displays the defaults
stored in nonvolatile memory as well as its default
configuration templates.

HELP SCREENS
The modem displays screens that summarize the command sets,
Dial command options, and S-register functions.

DIALING THE LAST-DIALED NUMBER
The modem has a buffer that stores each dialed number until
it is cleared by another Dial command.  A few keystrokes
cause the modem to redial the number in the buffer without
your having to enter the number again.

AUTOMATED REDIALING
You can put the modem into Repeat Mode to continuously
redial if a previous dial attempt fails to connect.  This is
especially useful in dialing services whose lines are often
busy.

QUOTE MODE
Set the modem to Quote Mode if you want it to dial an alpha-
betic acronym instead of a numeric number.






















COMPATIBILITY
------------------------------------------------------------

The Courier adheres to the following standards, ensuring
compatibility with a wide base of installed modems.  Unless
otherwise indicated, V.32 terbo and Dual Standard modems
both conform to the listed standards.

NOTE:  The International Telecommunication Union (ITU-T) was
formerly the International Telegraph and Telephone Consul-
tative Committee (CCITT).

USR-V.32 terbo      21.6K/19.2K/16.8K/14.4K/12K/9600/
                    7200/4800 bps  (Dual Standard and V.32
                    terbo modems)
USR-HST             16.8K/14.4K/12K/9600/7200/4800 bps (Dual
                    Standard modems in HST mode)
USR-HST Cellular    Cellular connections at 12K/9600/7200/
                    4800/2400/1200/300 bps  (Dual Standard
                    modems in HST mode)
ITU-T V.32 bis      14.4K/12K/9600/7200/4800 bps
ITU-T V.32          9600/4800 bps
ITU-T V.22 bis      2400 bps
Bell 212A           1200 bps (also V.22)
ITU-T V.23          1200 bps with 75 bps back channel
                    (optional, some United Kingdom and
                    European phone systems)
ITU-T V.25          Answer sequence for calls originating
                    outside the U.S. and Canada
Bell 103            300 bps (ITU-T V.21 optional)
ITU-T V.42          LAPM error control, 1200 bps and higher
ITU-T V.42 bis      Data compression, 1200 bps and higher
MNP                 Levels 2, 3 and 4 error control, level 5
                    data compression, 1200 bps and higher
ITU-T V.54          Analog, digital and remote digital
                    loopback testing


















FAX STANDARDS
-------------
The Courier modem provides Group III-compatibility when
combined with Class 1 or Class 2.0 fax software.  In
addition, the modem adheres to the following standards.
TIA/EIA-578    Service Class 1 Asynchronous Facsimile DCE
               Control Standard
TIA/EIA-592    Service Class 2.0 Asynchronous Facsimile
               DCE Control Standard
ITU-T V.17     14.4K/12K bps
ITU-T V.29     9600/7200 bps
ITU-T V.27 ter 4800/2400 bps
ITU-T V.21     300 bps

Other compatibility features include the following standards
and certification:
#    Can be used with any 100% IBM PC-compatible computer.
#    Is fully UL-listed, FCC- and DOC-certified for the uses
     described in this manual.



































+----------------------------------------------------------+
|                                                          |
|   CHAPTER 2.  SET-UP AND TESTING                         |
|                                                          |
+----------------------------------------------------------+

PACKAGE COMPONENTS
------------------------------------------------------------

Your Courier modem package contains the following items in
addition to this manual:
#    The modem you purchased.
#    An RJ-11-C phone cord.
#    A Quick-Reference card.
#    A STOP guide.  The guide contains DIP switch settings
     and other tips for using a number of popular
     communications software products.
#    Your warranty card, to be filled out and returned to
     U.S. Robotics, Inc.

OPERATIONAL REQUIREMENTS
------------------------------------------------------------

The Courier modem has minimal operational requirements.
Should you need it, you'll find information about radio and
television interference, and connecting to the phone
company, after the table of contents, at the beginning of
the manual.  In addition, you should be aware of the
following:

#    Review the instructions for Dedicated or Leased Line
     Operations in Appendix E, if the modem will be attached
     to a user-installed phone line or a line leased from
     the telephone company.  Often referred to as dedicated
     or private, this type of line is used for a direct,
     continuous connection between two modems.  The
     connection is made without dialing.

#    If the computer is installed in a Hewlett Packard
     system, be sure to follow the instructions in Appendix
     E, Hewlett Packard Installations.

COMMUNICATIONS SOFTWARE REQUIREMENTS
------------------------------------------------------------

You'll need communications software to operate the modem.
Communications software makes it possible for your computer
to send and receive data via the modem and phone lines.  It
also interacts directly with the modem.  Many excellent
compatible programs are available, all based on the AT
command set.

Some users prefer their communications software to take
control of the modem, and are more comfortable with a
program that makes the modem almost transparent.  Others 
prefer a program that allows them to use the modem's AT
command set sometimes, and their software commands or menus
at other times, depending on the task at hand.

BEFORE INSTALLING THE MODEM
------------------------------------------------------------
A typical new modem user has a PC with a printer connected
to the PC's parallel printer port, and a mouse whose cable
is attached to the PC's first serial port.  For this user,
the modem is the only device that requires a second serial
port.  If this is your situation, you can skip this entire
section except for DIP Switches, just before Installing the
Modem.  Just remember that after you load your
communications software, you'll have to set the software to
use the COM2 serial port.

IBM PC-compatible serial ports are referred to as COM ports.
Two COM ports are standard:  COM1 and COM2.  DOS recognizes
up to four COM ports, although more can be programmed.  The
Courier is set at the factory to use COM2.  This is because
many computers are shipped with COM1 equipped with an
external serial connector for attaching a device such as a
serial printer or serial mouse.  If you have a serial mouse
or serial printer, you're already familiar with COM ports on
a PC.

If you're only using COM1 for a device, you can skip this
section except for DIP Switches, just before Installing the
Modem.  If you've already installed devices at both COM1 and
COM2, you will have to select either COM3 or COM4.
Carefully review the following section for complete
instructions.

SELECTING A SERIAL PORT
------------------------------------------------------------

Using COM1, 2, 3 or 4 depends on your equipment's configura-
tion, as described below.  Remember which serial port you
assign to the modem, because you must specify it to your
communications software later.  The table in the next
section includes hexadecimal addresses, required by some
software.

COM1:  You may use this port if the computer does not have
an installed serial connector at COM1.  (This situation is
unlikely.)  You will have to modify some switches on the
modem, so read all of the following instructions.  However,
you may prefer to leave the modem set to COM2 and proceed to
DIP Switches, just before the installation instructions.
Later, set your software to COM1 or COM2, according to your
choice.

COM2:  If your computer is equipped with one serial con-
nector at COM1, and if you are not already using COM2 for
another device, use this port.  (This is the most common
configuration.)  Since the modem is already set to operate
at COM2, skip the rest of this section and proceed to DIP
Switches, just before the installation instructions.

COM3, COM4:  If you have two serial devices that already use
COM1 and COM2, you can set the modem for either COM3 or
COM4.  Review your communications software documentation to
be sure your program supports these additional serial ports.
(Most programs do.)  If your software doesn't, you will have
to remove one of the other devices.

NOTE:  If you are going to use COM1, COM3, or COM4, you must
change some switches on the modem board, called jumpers.
First, you need to select the correct Interrupt Request
(IRQ) to use at that serial port.  Peripheral devices use
IRQs to instruct the computer to stop the processor's cur-
rent operation; this allows the devices to perform their
operations.

SELECTING AN INTERRUPT REQUEST (IRQ)
------------------------------------------------------------

IBM-compatible computers reserve IRQ4 for COM1 and IRQ3 for
COM2, as shown in the table below.  All communication
programs support these reserved IRQs for those two serial
ports.

     Serial                        Serial Port
     Port           IRQ            Address (Hex)
     -------------------------------------------
     COM1           IRQ4           3F8+3FF
     COM2           IRQ3           2F8+2FF
     COM3           IRQ4*          3E8+3EF
     COM4           IRQ3*          2E8+2EF

*Select IRQ4 (COM3) or IRQ3 (COM4) only after reading the
following guidelines.

If you need to use COM3 or COM4, keep the following informa-
tion in mind.

#    The Courier allows three additional IRQs:  IRQ2, IRQ5
     and IRQ7.  Your software must support the one you use
     for COM3 or COM4.  However, if your computer is XT-
     compatible, IRQ5 is reserved for the hard disk, and it
     is not available for a serial port.  IRQ5 is available
     on 386-PCs and higher.

#    Two devices should not use the same IRQ at the same
     time, because there will be a conflict and you will
     probably lose data.  For example, if you use IRQ4 for a
     mouse installed at COM1 and for your modem installed at
     COM3, as shown in the previous table, you cannot use
     the mouse and the modem at the same time.

Additionally, if an installed device doesn't use IRQs, you
can use the IRQ normally associated with that COM port.  For
example, if you have a serial printer at COM1 and you know
it does not use an IRQ, you can use IRQ4 at COM3.
Similarly, you could use IRQ3 at COM4 if the device at COM2
doesn't use IRQ3.

If you cannot find the information you need in your software
documentation, call your software's Technical Support
Department for help in selecting an IRQ.  You may find it
necessary to re-install your serial devices to correctly
allocate the available serial ports and IRQs.

Resetting the Jumpers
---------------------
If you hold the modem so that the rear panel is at the
bottom and the edge connector is at the left of the circuit
board you can locate the COM and IRQ jumpers near the center
left side the board.

Each jumper has two upright contacts connected by a black
plastic piece, called shunts, placed over the contacts for
the COM2 and IRQ3 settings.  This shunt selects the jumper
by closing the circuit.

To change a jumper setting, gently lift off the black shunt
and replace it over the contacts you want.

As we've said, your choice of an IRQ for COM3 or COM4
depends on your hardware/software configuration.  If the
device at COM1 or COM2 isn't using IRQ4 or IRQ3, you may use
one of them.  Otherwise, check your PC and software
documentation to see if you may use IRQ2, IRQ5 or IRQ7.

WARNING:  Do not select an IRQ position until you've read
the previous guidelines and reviewed your software docu-
mentation.  The positions for alternative IRQs are shown
only to demonstrate the correct shunt placement for users
who are able to use them.

DIP Switches
------------
A ten-position bank of Dual In-Line Package (DIP) switches
is at the rear of the modem.  A summary of the DIP switch
functions and options is in Appendix B in this manual and in
the Quick Reference Card.

The STOP guide that came with the manual shows the correct
switch settings for many widely-used communications software
products.  If your communications software is not listed,
check your software documentation for its requirements,
particularly for switches 1, 4, 5 and 6.

DIP switch 10, used to load power-on and reset defaults, is
also explained under Setting/Using Defaults in Chapter 3.
Most users will want to leave this switch OFF, write their
own defaults to nonvolatile memory (NVRAM), and have those
defaults loaded at power on.

NOTE:  Once the modem is installed, the DIP switches are
accessible through the computer's rear panel.

INSTALLING THE MODEM
------------------------------------------------------------
1.   Turn off the computer and peripheral devices.

2.   Remove the computer's cover.  Refer to the computer
     manual, if necessary, to see which rear panel screws to
     remove before sliding the cover off.

3.   Unscrew the solid bracket at the back of any available
     expansion slot.  (The modem board requires at least a
     standard half-card slot.)

     The bracket will pop out of the back, leaving an
     opening in the rear panel for access to the modem's
     phone jacks and DIP switches.

4.   Expansion slots have either a 3-inch-long groove, or a
     3-inch and a 2-inch groove.  These grooves are lined on
     both sides with metal guides.  Insert the modem board
     into the slot you've chosen, with the leads on the
     modem board's edge connector firmly in the 3-inch
     groove.

5.   Screw the vertical bracket at the back of the modem
     firmly to the computer's rear panel.  This helps block
     radio frequency emissions from the computer and keeps  
     the modem board firmly in place.

6.   Replace the cover of the computer and replace the
     screws.

7.   If you currently have a phone plugged into the wall
     jack, disconnect it.  Plug one end of the phone cable
     that came with the modem into the TELCO jack at the
     rear of the modem.  This allows the modem to switch
     into the telephone network, get a dial tone, and so on.
     Plug the other end of the cable into the wall jack.

     NOTE:  The phone cable is equipped with two standard,
     modular RJ-11-C phone connectors.  If you have an older
     type of wall jack, you can purchase an adapter and RJ-
     11-C connector from your phone company or computer
     dealer.

8.   If you wish, plug your phone's cord into the second
     jack on the modem, labeled PHONE.  This enables you to
     use your phone for conventional voice calls, and also
     allows you to switch between voice and data trans
     mission in the same call.  See Voice/Data
     Communications in Appendix E for more information.

TESTING THE INSTALLATION
------------------------------------------------------------

Follow these steps to verify that the modem is working
properly.

1.   Load your communications software.  Set the serial port
     rate to 38,400 bits per second (or "baud rate," for
     some software).  The modem will detect this rate
     automatically when you send it a command.  If your
     software and computer both support 57,600 bps or
     115,200 bps, you can set your serial port to those
     speeds.

2.   Specify the serial port used by the modem, COM1, 2, 3
     or 4.

3.   Set the data format to a word length of either 7 bits
     plus Even or Odd parity, or 8 bits with no parity--it
     doesn't matter which for now--and 1 Stop bit.  Some
     programs use formats such as 7-E-1 or 8-N-1 for these
     three parameters.

4.   Perform the software function that lets you send AT
     commands directly to the modem, that is, puts the
     computer in Terminal mode.  Some communications
     programs do this automatically upon loading.  Others
     require you to display a communications or terminal
     screen, press a Function key, or perform some other
     operation.  If necessary, refer to your software docu-
     mentation for instructions.

5.   Check to see if your computer and modem are communi-
     cating with each other by sending the modem the fol-
     lowing attention command.  Type either upper or lower
     case letters, not a combination, and then press the
     Enter (Carriage Return) key, shown in the example below
     between angle brackets.  (Don't type the angle
     brackets.)
          AT <Enter>

     If everything is correct, the modem responds as
     follows.
          OK

     NOTE:  The modem is shipped with DIP switch 4 OFF,
     causing the modem to display (echo) your keyboard
     commands.  If your entered command is not displayed,
     your local echo is OFF.  To turn local echo ON, type
     the following command.
          ATE1 <Enter>

     If double characters appear on the screen, both your
     modem and software are set to local echo ON.  Either
     set your software to local echo OFF, or turn the
     modem's echo OFF with the following command.
          ATE0 <Enter>

TROUBLESHOOTING
------------------------------------------------------------
If no OK appears on your screen, review these checkpoints to
try to correct the problem.  Then try the AT command again.

a.   Make sure you type either all upper case (AT) or all
     lower case (at) letters and press <Enter>.

b.   Check to see that you set your communications software
     to the correct serial port.

c.   Make sure your software has put the computer in
     Terminal mode, so that you can send the modem commands.
     Review Step 4 on the previous page.

d.   Be sure that DIP switches 1 and 6 are set ON or OFF,
     according to your software requirements.  Check the
     STOP guide that came with the modem, or review the DIP
     switch table in Appendix B and your communications
     software documentation if you're unsure.

e.   If you set DIP switch 8 OFF for Dumb mode, switch it ON
     to reset the modem to Smart mode.

f.   DIP switch 3 controls the display of the modem's result
     codes, including the OK result.  The modem is shipped
     with DIP switch 3 ON, enabling the result codes.  If
     DIP switch 3 is OFF, reset it to the ON position and
     then initiate the new switch setting with the following
     reset command, and try typing AT <Enter> again.
          ATZ <Enter>

Checking the Phone Connection
-----------------------------
Make a final check of the modem to see that it gets a dial
tone.  Type the following manual Dial command.
          ATD <Enter>

Upon receiving the command, the modem goes off hook and
waits for a dial tone.  You'll hear the dial tone from the
modem's speaker.  To cancel the operation, press any key.

If you don't hear a dial tone, check to see that the phone
cable from the wall jack is connected to the jack labeled
TELCO on the modem.  If necessary, reconnect the phone cable
correctly, and try the ATD command again.

Be sure to return the modem on hook by pressing any key.
















































+----------------------------------------------------------+
|                                                          |
|   CHAPTER 3.  DATA MODE OPERATIONS                       |
|                                                          |
+----------------------------------------------------------+


     Detailed command descriptions are in this chapter.
     Additional command summaries are in the Quick-Reference 
     Card.

COMMAND SET USAGE
------------------------------------------------------------

     The Courier command set enables you to send the modem
     two kinds of instructions:
     #    operations, such as dialing or hanging up
     #    configurations, such as enabling error control or
          data compression

     Follow these guidelines:
     1.   Your software must be loaded and your computer or
          terminal must be in Terminal mode.

          In Terminal mode the computer acts as if it were a
          standard terminal such as a teletypewriter, rather
          than a data processor.  Keyboard entries go
          directly to the modem, whether the entry is a
          modem command or data to be transmitted over the
          phone lines.  Received data is output directly to
          the screen.  The more popular communications
          software products place the computer in terminal
          mode when the software is loaded.

     2.   Type commands in either upper or lower case, not a
          combination.

     3.   All commands except A/, A> and +++ are preceded by
          the AT prefix and are executed with the
          Enter/Carriage Return key (<Enter>).

     4.   Command length = 40 characters maximum.  The modem
          doesn't count the AT prefix, Carriage Return
          character, or spaces.  It counts but doesn't act
          on punctuation such as hyphens and parentheses.

     5.   A missing numeric parameter is assumed to be zero,
          as in the command to hang up:  ATH <Enter> is the
          equivalent of ATH0 <Enter>.

          Example (spaces are not required, but are added
          here for readability):
          AT &K3 X2 DT 071 312 1234 <Enter>

Meaning:
     AT     Get ready to execute the following commands.
     &K3    Disable MNP5 data compression, use only V.42 bis
            compression.
     X2     Use the X2 result code subset.
     DT     Dial the following phone number using tone
            dialing.
     <Enter> Execute the commands.

     This chapter groups related commands into the following
     categories.

     #    Basic Commands
     #    Dialing/Answering
               Dialing
               Dial Options
               Store Phone Numbers
               Redialing
               Answer Mode
               Auto Answer
               Hanging Up
     #         Setting/Using Defaults
               Resetting the Modem
     #    Configuration:
               Echo/Speaker
               Result Codes
               Modulation
               Error Control/Data Compression
               Data Rates
               Computer/Modem Signal Operations
               Flow Control
     #    S-Registers
     #    Inquiry and Help
     #    Testing
     #    International Calls
     #    Miscellaneous Commands
     For an alphabetical listing of commands, check the
     first page of the index.

     NOTE:  The defaults listed are based on the modem's
     shipping configuration:  load from nonvolatile random
     access memory (NVRAM), DIP switch 10 OFF, which is the
     same as the &F1 configuration template).  For a
     complete listing of default configuration templates,
     see Appendix B.









BASIC COMMANDS
------------------------------------------------------------

AT   Attention command prefix.  Use AT alone to test for the
     OK result code.  AT must prefix all commands except A/,
     A> and +++.
Any  Terminate the current dialing operation resulting from
key  an issued Dial command; terminate Repeat mode (> or
     A>).

DIALING/ANSWERING
------------------------------------------------------------
Dialing
-------
Dn   Dial the specified phone number; also execute Dial
     options.

     The maximum number of characters allowed is 36,
     including the AT prefix, punctuation and spaces.  The
     Carriage Return (Enter key) isn't counted as a
     character.

     NOTE:  With the exception of the following Dial
     options, the modem ignores any commands issued after D
     in the same command string.

Dial Options
------------
     D    Dial the number that follows and enter Originate
          mode.

Optional parameters:
     P    Pulse dial (Default).

     T    Tone dial.

     ,    (Comma) Pause for 2 seconds before continuing to
          dial.

     ;    Return to Command mode after dialing.  If your
          phone is plugged into the modem, you can use this
          option to have the modem Auto Dial a telephone
          rather than a modem.  The Courier dials, remains
          off hook and returns the OK message, indicating it
          is in Command mode.

          For example, to have the modem place a voice call,
          enter the Dial command with a semicolon:
               ATDT5551234; <Enter>

          When the modem returns the OK result, pick up your
          phone receiver so you can talk to the other party,
          and send the command that hangs up the modem:
               ATH <Enter>

     "    Dial the letters that follow (in an alphabetical
          phone number).  NOTE:  If you are including
          another command after the dial string, use closing
          quotation marks before the additional command.
     !    Transfer a call (flash the switch-hook).  This
          command applies to modems in installations where
          other modems share the phone line.  The modem
          flashes the switch-hook (goes off hook 0.5
          seconds, on hook for 0.5 seconds and off
          hook again) to dial the specified extension.

     W    This command is useful in situations where you
          must wait for a second dial tone before continuing
          dialing.  For example, if you need to dial for an
          outside line, the Courier continues dialing as
          soon as it detects the next dial tone.
               AT DT 9 W 5551234 <Enter>

          NOTE:  This command executes only if result code
          option X3 or greater has been issued.  If the
          modem is set to X2 or lower, the modem interprets
          the W as a comma (two-second pause).

     @    Wait for an answer (with X3 or higher).  Some
          online services answer the phone and return a
          tape-recorded request for information before
          processing transactions.  In such instances, the @
          command can be used in the Dial string to tell the
          modem to detect at least one ring, wait for five
          seconds of silence at the other end of the call,
          and then continue to execute the Dial string.

          To use the @ command, set the modem to X3, X4 or
          X7.  If the modem is set to X2 or lower, the modem
          returns an ERROR message when encountering the @
          character in a command string.  If set to X5 or
          X6, the modem hangs up when it detects a voice
          answer and sends the VOICE result code.

     /    A slash (/) causes a pause of only 125
          milliseconds.

     R    Reverse frequencies.  This command allows calls to
          an originate-only modem.  It reverses the modem's
          originate/answer frequencies, forcing the Courier
          to dial out at the answer frequency.  The command
          follows the Dial command, before or after the
          phone number:
               AT D1234567R <Enter>

     X2-X7   Adaptive dialing.  When any of the X2 through
          X7 options is in effect and you do not issue a
          dialing type in the Dial string, the Courier uses
          tone dialing, which is faster than the default
          pulse type.  However, if the phone company's
          central office does not have tone detection
          equipment, the modem cannot break dial and
          continues to detect the dial tone.  If this
          occurs, the modem automatically reverts to pulse
          dialing.

DL   Dial the last-dialed number.  The modem stores each
     Dial command until it receives the next Dial command.
     Use DL instead of A/, described on the next page, if
     you wish to send the modem non-Dial commands before
     dialing again.

DSn  Dial the number stored in nonvolatile random access
     memory at position n, where n = 0-9.

Store Phone Numbers
-------------------
&Zn=s This command stores up to ten numbers, where n is the
     position 0-9 in nonvolatile memory, and s is the phone
     number string.  The number-string may be up to 36
     characters long, including any Dial command options.
               AT &Z2=555-6789 <Enter>

     Do not include modem settings in the &Zn string.  If
     the call requires a special setting, insert it in the
     command string before the DSn command.  In the
     following example, &M0 (no error control) is inserted
     before the Dial command:
               AT&M0 DS2 <Enter>

     NOTE:  The &Zn=s command functions differently when
     Dial Security is enabled.  See Appendix C for more
     information.

&Zn? Display the phone number stored in NVRAM at position n
     (n = 0-9).

Cancel Dialing
--------------
     To cancel Dial-command execution, press <any key>. If
     you inadvertently hit a key on the keyboard while the
     modem is dialing, the call is canceled.  If this
     occurs, type the A/ command explained under Automated
     Redialing later.

     When the modem receives a command, it stores the
     instruction in its command buffer until it receives the
     next AT command.  Note that if you've sent the modem an
     additional command since the Dial command, A/ re-
     executes that command instead of redialing.


Redialing
---------
A/   Re-execute the last issued command.  A/ doesn't take
     the AT prefix or a Carriage Return, and can be used to
     redial.
               A/

               Automated Redialing (>, A>)
     While > and A> can be used to continuously repeat any
     command, they are designed for automated redialing.

Enter Repeat Mode
>    If you know the modem you are calling is frequently
     busy, include the Repeat command in the Dial string, as
     follows:
               AT > DT 1234567 <Enter>  or
               AT DT 1234567 > <Enter>

     The modem enters Repeat mode, dials the number, waits
     60 seconds for a carrier (default), and hangs up.  Then
     after a two-second pause, it redials.

     The cycle continues until the modems connect or the
     modem reaches a maximum of 10 attempts.  The 10-try
     limit is mandated by the Canadian Department of
     Communications (DOC) to prevent tying up local
     telephone company exchanges with unconnected calls.

A>   This command combines the features of both the A/ and >
     commands.  The modem enters Repeat mode as described
     above, and redials the Dial string in the command
     buffer.  Like the A/ command, A> does not take the AT
     prefix or a Carriage Return.

Exiting Repeat Mode
-------------------
     Should you use > or A> with a command other than a Dial
     string, abort the cycle by pressing <any key>.  To
     abort automated redialing, be sure to press <any key>
     when the result code appears, during the pause before
     the modem begins dialing again.  If you press <any key>
     while the modem is dialing, that dial attempt is
     canceled but the cycle continues.

Answer Mode
-----------
Force Answer Mode
A    Force Answer mode when the modem hasn't received an
     incoming call.

Auto Answer
     The Courier is shipped with DIP switch 5 ON, Auto
     Answer suppressed.  To set the modem to automatically
     answer incoming calls, do one of the following:
     1.   Before powering on the modem, set DIP switch 5
          OFF.  When you turn the computer on, the modem
          answers incoming calls on the first ring.

     2.   When the modem is on, set your communications
          software to enable auto answer.  The following
          command instructs the modem to answer on the first
          ring.  (You can substitute a higher value.  See
          the S-Register summary in Appendix B.)
               AT S0 = 1 <Enter>

          When the modem senses a call coming in, it sends
          the result code RING to your screen, goes off
          hook, and sends the remote modem a high-pitched
          answer tone.  If there is no Carrier Detect within
          60 seconds, the modem hangs up. If the connection
          is made, the modem sends a CONNECT result code.

          When the call is disconnected by you or the remote
          user, the modem hangs up and returns the NO
          CARRIER code.

          NOTE:  If DIP switch 5 is OFF and S0=0, the Auto
          Answer will be disabled.  Be sure that S0=1+256.

Suppressing Auto Answer
-----------------------
          To disable Auto Answer, reverse Steps 1 or 2
          above.  Set DIP switch 5 ON before powering on the
          modem, or set the modem to answer on zero rings
          with the following command.
               AT S0 = 0 <Enter>

Points to Remember
     1.   If the modem is attached to a computer, you can
          set the modem to receive calls when you're not at
          your computer.  Load your communications software
          as you normally do, and set the modem to Auto
          Answer.  Also set your software's file-save
          function to save incoming messages and/or files.

     2.   If you've attached your phone so it can be used
          for conventional calls, disable Auto Answer when
          you are not expecting incoming data calls.
          Otherwise, your modem may answer the phone before
          you do, greeting a voice caller with a high-
          pitched, irritating answer tone.







Hanging Up
----------
Hn   On/off hook control.

     H0   Hang up (go on hook).

     H1   Go off hook.

     +++  Escape code operations.  Once the modem is online
          to another system, the only command it recognizes
          is an escape code of three typed pluses, which
          forces the modem back to Command mode.  Do the
          following when issuing the command:

     #    Wait one second after sending the last item of
          data
     #    Type: +++
     #    Wait one second before typing any data

     Do not type the AT prefix or a Carriage Return.  The
     guard time of one second before and after the code
     prevents the modem from misinterpreting the occurrence
     of +++ in the transmitted data stream.

     If necessary, the character used in the escape code or
     the duration of the guard time can be changed by
     resetting Register S2 or S12.  See the S-Register
     Summary in Appendix B.

     In response to +++ the modem returns to Command mode.
     However, it keeps the line open or hangs up, depending
     on the setting of DIP switch 9:

     DIP Switch 9   Response to +++
     -------------------------------------------------------
     OFF            Modem goes on hook (hangs up), sends NO
                    CARRIER result code (factory setting)
     ON             Modem maintains connection (Online-
                    Command mode), sends OK result code

     The factory setting (OFF) forces an automatic
     disconnect when you issue +++.   An advantage of this
     is that you are not likely to inadvertently run up an
     all-night phone bill.

     Set DIP switch 9 ON if you want the modem to respond to
     +++ by entering Online-Command mode, enabling it to
     execute commands and return online.  (See the O
     command, below.)

     WARNING:  For unattended modem operations:  in rare
     instances, the modem may fail to recognize the +++
     escape code sequence.  If you are running the modem
     under software control for unattended operations, we
     suggest you use the surefire method of dropping the DTR
     signal from the computer or terminal for at least 50
     milliseconds, to ensure against costly phone charges.
     Methods of turning the DTR signal off--for example,
     closing the communications port--differ from one
     computer to another.

Returning Online
----------------
On   If DIP switch 9 is ON (on detection of the escape code
     the modem maintains the connection), you can issue
     commands and then toggle the modem back online with the
     On command, as in this example:
               AT Q1 O <Enter>

     There are two ways to return online.

     ATO0 Return online (normal).  (Used in the example
          above.)

     ATO1 Return online and retrain.  Use to have the modem
          re-synchronize if there were errors in a non-ARQ
          data transfer.

Hanging Up
----------
     If DIP switch 9 is ON, the escape code forces the modem
     back to Command mode but leaves the line open.  If you
     want the modem to hang up, issue the following command
     once the modem sends the OK result code.
               ATH <Enter>

     If DIP switch 9 is OFF, the modem automatically hangs
     up on receipt of the escape code.

SETTING/USING DEFAULTS
------------------------------------------------------------

     The modem's read-only memory (ROM) permanently stores
     the modem's four factory template settings.  The
     inclusion of nonvolatile random access memory (NVRAM)
     allows you to save one of these four templates, or add
     your own modifications, and write all the settings to
     NVRAM as your power-on defaults.

&Fn  The modem is shipped with four configurations
     (templates), &F0+&F3, stored in permanent
     nonprogrammable memory (ROM).  Appendix B includes
     configuration listings for each template.  Any one of
     the templates may be loaded into current memory (AT
     &Fn) or written to nonvolatile memory and reset default
     (AT &Fn &W).  Note, however, that &F0 is always loaded
     into memory if DIP switch 10 is ON.

     When you power on the Courier, it loads the settings
     stored in NVRAM if DIP switch 10 is OFF.  Until you
     write your own settings to NVRAM, the defaults stored
     there are the same as the permanent ROM factory
     settings stored in position 1, &F1.

     To view the &F1 settings, select option 5 of the I
     (inquiry) command:
               AT I5 <Enter>

Customizing NVRAM
-----------------
&W   To substitute a template other than &F1, write the
     desired template to NVRAM, using the &W command.
               AT &F2 &W <Enter>

     To modify the &Fn configuration in NVRAM, type your
     changes and then save them to NVRAM, as in the
     following example.  The original factory template
     remains intact.
               AT M2 S10=40 &A2 &W <Enter>

     NOTE:  When writing a different default configuration
     to NVRAM, insert your addition after the &Fn command
     but before &W.  Otherwise they will be overwritten by
     &Fn.

     After sending a configuration to NVRAM, you can change
     any setting just for the current session, as in the
     following example.  The NVRAM configuration remains
     intact.
               ATX6 <Enter>

     But if you want the new setting to be a default, write
     it to NVRAM at the same time, as in the following
     example.  X7 is substituted for the Xn value stored
     earlier.  Any other setting that was changed and can be
     saved to NVRAM will also be saved.
               AT X7 &W <Enter>

Resetting the Modem
-------------------
Z    Software reset to NVRAM settings when DIP switch 10 is
     OFF (factory setting).  If DIP switch 10 is OFF, the
     modem resets to the &F0 configuration template, with no
     flow control.

     NOTE:  Use the ATZ command also if you've changed the
     position of DIP switches 1+7 or 9 while the modem is
     on, so that the modem can read the new setting.  The
     only other way to initiate a new setting for switches
     1-7 and 9 is to turn the modem off and on again.


CONFIGURATION
------------------------------------------------------------

Echo/Speaker
------------
En   Command mode local echo.  Enables/disables the display
     of your typed commands.  If double characters appear on
     the screen, both the modem's local echo and your
     software's local echo are on.

     The Courier is shipped with DIP switch 4 OFF, enabling
     local echo.  The En command controls the local echo for
     a current session, independently of the switch setting.
     At power-on and reset, the modem operates according to
     the DIP switch setting.  The En command is not stored
     in nonvolatile memory as a power-on/reset default.

     E0   Command mode echo OFF.  The modem does not display
          keyboard commands.

     E1   Command mode echo ON.

Fn   Online local echo.  This command causes the modem to
     display a copy of the data it is transmitting to
     another system.  Many systems, however, return a copy
     of received data, which is called a remote echo.  If
     the modem's online echo is ON and there is also remote
     echoing, double characters appear on the screen.

     In some microcomputer documentation, the term duplex is
     applied to local online echoing, although the term is
     not technically accurate.

     F0   Online echo ON.  Sometimes called half duplex.  As
          the modem transmits data to a remote system, it
          also sends a copy of the data to the screen.

     F1   Online echo OFF.  Sometimes called full duplex.
          Default.

Ln   Speaker volume control.

     L0   The volume from the speaker is low.

     L1   Same as L0.  The volume from the speaker is low.

     L2   The volume from the speaker is medium.

     L3   The volume from the speaker is high.

Mn   Speaker (audio monitor).

     M0   The speaker is always OFF.

     M1   The speaker is ON until carrier is established
          (Default).

     M2   The speaker is always ON, including during data
          transfer.

     M3   The speaker is ON after the last digit is dialed
          and remains ON until carrier is established.

Result Codes
------------
Qn   Enable/suppress the display of result codes.  The
     Courier is shipped with DIP switch 3 ON, to display
     result codes.  Use the Qn command to control the
     display for a current session, independently of the
     switch setting.

     At power-on and reset, the modem operates according to
     the DIP switch setting.  The Qn command is not stored
     in nonvolatile random access memory.

     Q0   Result codes displayed.

     Q1   Result codes suppressed (quiet).

     Q2   Result codes suppressed in Answer mode.

Vn   Return result codes in words or numbers (Verbal/Numeric
     mode). At power-on and reset, the modem operates
     according to the DIP switch setting.  The Vn command is
     not stored in nonvolatile memory as a power-on/reset
     default.

     V0   Numeric mode.

     V1   Verbal mode.


















Xn   Result code set options.  Use the following table.
     (Default = X7, all codes except 12/VOICE).  For result
     codes in synchronous operations, see Appendix I.

          Setting
Result Codes   X0   X1   X2   X3   X4   X5   X6   X7
----------------------------------------------------------
0/OK           *    *    *    *    *    *    *
1/CONNECT      *    *    *    *    *    *    *    *
2/RING         *    *    *    *    *    *    *    *
3/NO CARRIER   *    *    *    *    *    *    *    *
4/ERROR        *    *    *    *    *    *    *    *
5/CONNECT 1200      *    *    *    *    *    *    *
6/NO DIAL TONE           *         *         *    *
7/BUSY                        *    *    *    *    *
8/NO ANSWER                   *    *    *    *    *
9/RESERVED
10/CONNECT 2400     *    *    *    *    *    *    *
11/RINGING                              *    *    *
12/VOICE                                *    *
13/CONNECT 9600     *    *    *    *    *    *    *
18/CONNECT 4800     *    *    *    *    *    *    *
20/CONNECT 7200     *    *    *    *    *    *    *
21/CONNECT 12000    *    *    *    *    *    *    *
25/CONNECT 14400    *    *    *    *    *    *    *
43/CONNECT 16800    *    *    *    *    *    *    *
85/CONNECT 19200    *    *    *    *    *    *    *
91/CONNECT 21600    *    *    *    *    *    *    *

Functions
Adaptive Dialing         *    *    *    *    *    *
Wait for 2nd Dial Tone (W)    *    *    *    *    *
Wait for Answer (@)           *    *    *    *    *
Fast Dial                *         *         *    *

               Table 3-1.  Result Code Options

NOTE:  Additional messages indicate an error control
connection and the modulation for a call.  See the
Additional Result Codes that follow.














Result Code    Meaning

------------------------------------------------------------
0/OK           Command has been executed.
1/CONNECT      Connection with another modem; if set to X0,
               connection may be between 300 and 21.6 bps;
               if X1 or higher, connection is at 300 bps.
2/RING         Incoming ring detected.
3/NO CARRIER   Carrier detect has failed or carrier has been
               dropped due to disconnect.
4/ERROR        Command is invalid.
5/CONNECT 1200 Connection with another modem at 1200 bps.
6/NO DIAL TONE Dial tone not detected during the normal 2
               seconds, set in Register S6.
7/BUSY         Busy signal detect; modem hangs up.
8/NO ANSWER    After waiting 5 seconds for an answer, modem
               hangs up; returned instead of NO CARRIER when
               the @ option is used.
10/CONNECT 2400   Connection with another modem at 2400 bps.
11/RINGING     The modem has dialed; remote phone line is
               ringing.
12/VOICE       Voice answer at remote site; modem hangs up.
13/CONNECT 9600   Connection at reported rate.  Same
               meaning for results of 4800 (18), 7200 (20),
               12K (21), 14.4K (25), 16.8K (43), 19.2K (85),
               or 21.6K (91).

Adaptive Dialing  The modem attempts to use tone dialing
               and, if that doesn't work, reverts to rotary
               dialing.

Wait for Another  The modem continues dialing as soon as
Dial Tone (W)  it detects another dial tone.  See the
               dial options earlier in this chapter.

Wait for an    The modem continues dialing when it detects 5
Answer (@)     seconds of silence on the line.  See the dial
               options earlier in this chapter.

Fast Dial      The modem dials immediately on dial-tone
               detect, instead of waiting the normal 2
               seconds set in Register S6.

               Table 3-2.  Result Code Definitions










ADDITIONAL RESULT CODE SUBSETS
------------------------------------------------------------

     NOTE:  ARQ (Automatic Repeat Request) is used in this
     manual to denote calls under error control.

&An  Enable/disable additional result code subsets.  See the
     Xn command earlier in this chapter.

     &A0  ARQ result codes are disabled.  This setting does
          not affect an error control connection; the modem
          returns the standard CONNECT messages if result
          codes are enabled.

     &A1  ARQ result codes are enabled, indicating that a
          connection is under error control.  Message 14 is
          displayed if the modem is set to X0 and the
          connection is at any rate from 1200 to 21.6K bps.
          The remaining results indicate the connection rate
          and require a setting of X1 or higher.

     14/CONNECT/ARQ      24/CONNECT 7200/ARQ
     15/CONNECT 1200/ARQ 26/CONNECT 14400/ARQ
     16/CONNECT 2400/ARQ 47/CONNECT 16800/ARQ
     17/CONNECT 9600/ARQ 88/CONNECT 19200/ARQ
     19/CONNECT 4800/ARQ 94/CONNECT 21600/ARQ
     22/CONNECT 12000/ARQ

     &A2  Additional HST or V32 modulation indicator.
          Included for users of HST Dual Standard modems.
          If your software cannot handle the added
          modulation information, select &A1 or &A0.

     23/CONNECT 9600/HST      or   33/CONNECT 9600/V32
     27/CONNECT 9600/ARQ/HST  or   37/CONNECT 9600/ARQ/V32
     28/CONNECT 4800/HST      or   38/CONNECT 4800/V32
     29/CONNECT 4800/ARQ/HST  or   39/CONNECT 4800/ARQ/V32
     30/CONNECT 7200/HST      or   40/CONNECT 7200/V32
     34/CONNECT 7200/ARQ/HST  or   44/CONNECT 7200/ARQ/V32
     31/CONNECT 12000/HST     or   41/CONNECT 12000/V32
     32/CONNECT 12000/ARQ/HST or   42/CONNECT 12000/ARQ/V32
     35/CONNECT 14400/HST     or   45/CONNECT 14400/V32
     36/CONNECT 14400/ARQ/HST or   46/CONNECT 14400/ARQ/V32
     53/CONNECT 16800/HST     or   83/CONNECT 16800/V32
     57/CONNECT 16800/ARQ/HST or   84/CONNECT 16800/ARQ/V32
     88/CONNECT 19200/ARQ     or   87/CONNECT 19200/V32
                              or   90/CONNECT 19200/ARQ/V32
     94/CONNECT 21600/ARQ     or   93/CONNECT 21600/V32
                              or   96/CONNECT 21600/ARQ/V32

     &A3  Additional error control indicator (LAPM, HST,
          MNP, SYNC, or NONE) and data compression type
          (V42BIS or MNP5).  Default.  When the call is not
          under one of those protocols (and ARQ is not
          included in the result code), the modem reports
          either SYNC, indicating a synchronous connection,
          or NONE, for no protocol.
          If the modems are using data compression, the type
          of compression, V42BIS or MNP5, is added to the
          result code.  In the first of the following
          examples, the modems negotiated error control for
          the call (ARQ), used V32 modulation, are using the
          LAPM error control protocol, and are using V.42
          bis compression.

     CONNECT 21600/ARQ/V32/LAPM/V42BIS  [or MNP/MNP5]
     CONNECT 19200/ARQ/V32/LAPM/V42BIS  [or MNP/MNP5]
     CONNECT 19200/SYNC
     CONNECT 16800/ARQ/V32/LAPM/V42BIS  [or MNP/MNP5]
     CONNECT 16800/ARQ/HST/HST/V42BIS  [or MNP/MNP5]
     CONNECT 16800/SYNC
     CONNECT 14400/SYNC
     CONNECT 12000/ARQ/HST/HST/CELLULAR/V42BIS  [or MNP5]
     CONNECT 12000/SYNC
     CONNECT 9600/SYNC
     CONNECT 2400/ARQ/MNP/MNP5  [or LAPM/V42BIS]
     CONNECT 2400/NONE

     NOTE:  Although these codes will return numeric identi-
     fiers, they are the same numeric identifiers used for
     &A2 result codes.  If the modem is in Numeric mode (V0)
     and set to &A3, you will not be able to differentiate
     between &A2 and &A3 result codes.  &A3 result codes may
     not be compatible with some software.

Modulation
----------
Bn   Handshake options.  There are three commands that apply
     to international calls above 1200 bps--Bn, &Gn, &Pn.
     See International Calls later in this chapter for
     information on the other two settings.

     B0   ITU-T (formerly CCITT) answer sequence.  Default.
          This is required to answer all V.32-type calls as
          well as calls from overseas.

     B1   Bell answer tone.  This setting selects HST
          modulation in Dual Standard modems; but should
          only be used if the modem is not required to
          answer V.32-type calls, because it sends the wrong
          answer tones.  NOTE:  This setting is used for HST
          cellular calls.






Error Control/Data Compression
------------------------------
&Mn  Enable ARQ (error control) or synchronous protocols.
     Both your modem and the remote modem must use the same
     protocol.

     &M0  Normal mode, no error control.  Due to the nature
          of phone line channels, this is never recommended
          for calls above 2400 bps.

     &M1  This setting is exclusive of the modems' error
          control and is used only for online synchronous
          mode without V.25 bis.  See Appendix E for more
          information .

     &M2  Reserved.

     &M3  Reserved.

     &M4  Normal/ARQ mode.  Default.  If an ARQ connection
          isn't made, the modem operates in Normal mode, as
          though it were set to &M0.

          NOTE:  V.32-type modems reverting to Normal mode
          transfer data at high speeds without the
          reliability of error control.  To avoid this,
          these modems, local and remote, should always be
          set for error control.  Modems in HST mode, if
          unable to establish an error control connection,
          drop to 2400 bps.

     &M5  The modem enters ARQ asynchronous mode.  The modem
          hangs up if an ARQ connection cannot be made.

     &M6  The modem enters V.25 bis synchronous mode, using
          a character-oriented link protocol similar to
          BISYNC.  See Appendix E for more information

     &M7  The modem enters V.25 bis synchronous mode, using
          the HDLC link protocol.

&Kn  Enable/disable data compression.

     &K0  Data compression disabled.

     &K1  Auto enable/disable.  Default.  The modem enables
          compression if the serial port rate is fixed, &B1,
          and disables compression if the serial port rate
          allows the connection rate, &B0, because
          compression offers no throughput advantage when
          the serial port and connection rates are equal:
          compression may even degrade throughput.

     &K2  Data compression enabled.  Use this setting to

          keep the modem from disabling compression.

     &K3  Selective data compression.  The modem negotiates
          only for V.42 bis compression, and disables MNP
          Level 5 (MNP5) compression.  Use this setting to
          transfer 8-bit binary files, .ZIP files, and other
          files that are already compressed.  See the note
          below.

          NOTE:  MNP5 compression is not useful when
          transferring files that are already compressed,
          such as the .ZIP files downloaded from many
          Bulletin Boards and 8-bit binary files, which
          appear to the modem to be compressed.  MNP5 tends
          to add data to the transmission so that throughput
          over the link degrades.  V.42 bis compression
          dynamically detects when data is already
          compressed and turns off until it detects that
          compression will work to advantage.  The special
          &K3 setting enables the best throughput for
          already-compressed files.

     See Throughput Guidelines and Data Compression in
     Appendix A for more information, including throughput
     to expect for different kinds of files.

Data Rates
----------
     The modem can be set to a fixed or variable serial port
     rate.  A fixed rate sets the modem for the highest
     possible throughput and provides the best performance.
     A variable rate allows the modem to switch to match the
     more limited rate on the phone connection.

     Your software must support fixed or variable serial
     port rates, and must be set to either of the two
     settings.  NOTE:  Your software may refer to these
     options with terms like locked serial port (fixed rate)
     or autobaud (variable rate).

     Most communications programs support variable rates,
     but not all software supports fixed rates.

     WARNING:  To connect above 9600 bps, the serial port
     rate must be 19.2K, 38.4K, 57.6K, or 115.2K bps.  If
     the local computer is limited to 9600 bps, V.32 terbo
     modems are limited to 9600 bps maximum, that is, V.32.
     Disable V.32 terbo modulation so that the modem does
     not switch its serial port rate up higher than 9600
     bps.  Do this by setting Register S34 to 3 (S34=3) and
     including that setting in the defaults you write to
     nonvolatile memory, as shown in Setting/Using Defaults
     earlier in this chapter.

&Bn  Serial port rate variable or fixed.

     &B0  Variable rates.  When the modem switches its
          connection rate to connect with a modem operating
          at a different rate, it also switches its serial
          port rate.  The software or terminal also switches
          serial port rates to match the connection rate.

     &B1  Fixed rate.  Default.  The modem always
          communicates with the terminal or computer at the
          rate at which you have set the terminal or
          software, regardless of the connection rate.  For
          the greatest throughput, set the serial port to
          115.2K, 57.6K, 38.4K bps for high speed calls and
          to at least 9600 bps for 2400-bps calls.

          This setting is not affected by the &N setting.
          However, the serial port rate must be equal to or
          higher than the &Nn rate.

     &B2  Fixed for ARQ calls/Variable for non-ARQ calls.
          Answer mode only.  When the modem goes off hook
          and connects in ARQ mode, it shifts its serial
          port rate up to a user-specified rate, for
          example, 38.4K bps.  If the connection is not
          under error control, the modem behaves as if it
          were set to &B0 and switches its serial port rate
          to match the connection rate of each call.

          This option is designed for installations such as
          Bulletin Boards that receive calls from a wide
          variety of modems, ranging from the very slow to
          those with the Courier's advanced design.

          To implement this feature, first set your software
          to the desired rate.  Then send the modem the AT
          &B2 [other settings] &W command.

          The modem stores the rate of the command in NVRAM
          along with the settings.  Each time it makes an
          ARQ connection, the modem checks NVRAM for the
          specified serial port rate.

          When sending subsequent configurations to NVRAM,
          be sure your software is set to your selected
          serial port rate, so that the correct rate is
          maintained.

&Nn  Connection rate variable or fixed.

     &N0  Variable rates.  Default.  The Courier
          negotiates with the remote modem for the
          highest possible connection rate, depending
          on the capabilities of the remote modem.
          This is the recommended setting, and is required
          for the Courier V.32 terbo to connect at 21.6K
          bps.  Both modems must be U.S. Robotics modems
          with V.32 terbo to make a 21.6K bps connection.

     &N1- Fixed rate.  The modem only connects if the
     &N10 remote modem is operating at the same rate.
          If not, the modem hangs up.  If you wish, you can
          filter out calls at other than a specific rate,
          for security or other reasons, by fixing the
          connection rate.

          The connection rate must always be lower than, or
          equal to, the serial port rate, never higher.

          The options are as follows.
          &N1  300 bps   &N7  12K bps
          &N2  1200 bps  &N8  14.4K bps
          &N3  2400 bps  &N9  16.8K bps (HST+to+HST or
          &N4  4800 bps       terbo+to+terbo only)
          &N5  7200 bps  &N10 19.2K bps (terbo+to+terbo
          &N6  9600 bps       only)

Computer/Modem Signals
----------------------
&Cn  Carrier Detect operations.  At power-on and reset, the
     modem operates according to the setting of DIP switch
     6.  This command is not stored in nonvolatile memory as
     a power-on/reset default.

     &C0  CD override, CD always ON.

     &C1  Normal CD operations.  The Courier sends a CD
          signal when it connects with another modem and
          drops the CD when it disconnects.

&Dn  Data Terminal Ready (DTR) operations.  At power-on and
     reset, the modem operates according to the setting of
     DIP switch 1.  This command is not stored in non
     volatile memory as a power-on/reset default.

     &D0  DTR override.  The modem operates as though the
          DTR is always ON.

     &D1  Advance usage:  If issued before connecting with
          another modem, the modem can enter online command
          mode during a call by toggling DTR.  (Most
          communications software packages have a method for
          toggling DTR.)  &D1 functions similarly to the
          escape code (+++), except that this setting is
          independent of DIP switch 9.

          If DIP Switch 1 is ON (DTR override) when you
          issue the &D1 command, the DTR override is
          automatically turned off.  However, if you change
          the setting of DIP switch 1 after issuing &D1, the
          DIP switch setting takes precedence.

          Return online with the On command, or hang up with
          the Hn command.

     &D2  Normal DTR operations.  The terminal or computer
          must send a DTR signal for the modem to accept
          commands.  Dropping DTR terminates a call.

&Sn  The modem sends the computer or terminal a Data Set
     Ready (DSR) signal via the RS-232 interface.  (Data Set
     is industry jargon for modem.)  Few, if any, commercial
     communications programs require the modem to control
     DSR, &S1.  Leave the modem set for DSR overridden, &S0,
     unless you know that your installation requires a
     different setting.

     &S0  DSR is always ON (override).  Default.

     &S1  In Originate mode, the modem sends the DSR after
          it dials, when it detects the remote modem's
          answer tone.  In Answer mode, the modem sends the
          DSR after it sends an answer tone.

     &S2  This option is for specialized equipment such as
          automatic callback units.  On loss of carrier, the
          modem sends a pulsed DSR signal with Clear to Send
          (CTS) following Carrier Detect (CD).

     &S3  This is the same as &S2, but without the CTS
          following CD.

     &S4  The modem sends the computer a DSR signal at the
          same time as it sends the Carrier Detect (CD).

Flow Control
------------
     Flow control allows the modem to monitor the amount of
     data coming from the computer or the remote modem, and
     notify either end if its buffers are too full, so that
     they stop sending data for a moment.

     The modem uses either hardware or software flow
     control.  Your software and machine must support
     whichever type you select.

Hardware Control
     The modem drops the Clear to Send (CTS) signal it's
     been sending to the computer or terminal when the
     modem's buffer nears 90% capacity.  It starts sending
     CTS again when the buffer is about half full.

Software Control
     The modem sends the computer or terminal the standard
     ASCII Transmit OFF (XOFF) character, <CTRL-S>, when its
     buffer nears 90% capacity.  The  modem sends the ASCII
     Transmit ON character, <Ctrl>-Q, when the buffer is
     about half full.  ASCII definitions are as follows:

     XON      <Ctrl>-Q       (ASCII 17 Decimal, 11 Hex)
     XOFF     <Ctrl>-S       (ASCII 19 Decimal, 13 Hex)

     NOTE:  You should set your software as well to either
     hardware or software flow control.  Some programs also
     require that you turn off the type you are not using.

     The ASCII characters may be user-defined.  See
     Registers S22 and S23 in Appendix B.  That appendix
     also includes an ASCII chart.

     WARNING:  If possible, always use hardware flow
     control, the factory default.  You may lose data if
     XON/XOFF (Ctrl-S, Ctrl-Q) characters occur in the data
     stream from other sources.  They may, for example, come
     from the remote system:  an XON from the remote system,
     after your modem has sent an XOFF, can result in buffer
     overflow.

     Ctrl-S (XOFF) and Ctrl-Q (XON) characters also occur in
     binary files, and are used by Xmodem-type protocols.
     You risk having these characters misinterpreted as
     modem flow control characters and dropped from the data
     stream.

     If you cannot use hardware flow control and if you're
     transferring non-text (binary) files, or using an
     Xmodem-type protocol, disable flow control entirely
     (&H0).  In addition, be sure the modem is set to &B0
     and &N0, so that the serial port and connection rates
     are equal.

Transmit Data Buffer Sizes
--------------------------
     The Transmit Data refers to the data from the computer,
     which the modem is to transmit over the phone line.

     The size of the Transmit data buffer depends on whether
     the connection is under error control or not, as
     follows.

     #    ARQ connections:  3.25K bytes.
     #    Non-ARQ connections:  1.5K bytes, allowing use of
          error control file transfer protocols such as
          Xmodem and Ymodem without flow control.

     If bit 3 of Register S15 is turned on, the non-ARQ
     buffer size is reduced to 128 bytes, for the
     convenience of BBS operators taking calls from remote
     users of slower modems.  See S-Register Summary, S15,
     in Appendix B.

Received Data Buffer Size
-------------------------
     Received Data refers to the data the modem has received
     over the phone link, which the modem is to pass on to
     its attached computer.

     The size of this buffer remains constant at 2K bytes.

Transmit Data Flow Control
--------------------------
&Hn  This type of flow control is for data transmitted to
     the modem by its attached computer or terminal.  The
     modem monitors its buffer as data comes from the
     computer or modem.  If the buffer approaches 90%
     capacity, the modem signals the computer or terminal to
     stop transmitting.  When the modem has sent enough data
     over the link to half empty the buffer, it signals the
     computer or terminal to resume transmitting.

     &H0  Transmit Data flow control disabled.

     &H1  Hardware flow control.  Default.  Requires that
          your computer or terminal and software support
          Clear to Send (CTS) at the RS-232 interface.

     &H2  Software flow control.  Requires that your
          software support XON/XOFF signaling.

     &H3  Use both hardware and software flow control.  If
          you are unsure about what your equipment supports,
          select this option.  But keep the warning, above,
          in mind about software flow control.

Received Data Flow Control
--------------------------
     Separate commands, &Rn (hardware) and &In (software),
     control the flow of Received Data passed by the Courier
     to your computer or terminal.

     Your software and machine must support whichever type
     you select, although we recommend hardware flow
     control, if possible.

Hardware Control(&Rn)
---------------------
&R0  Delay Clear to Send Response after Request to Send
     signal (RTS/CTS delay).  The delay is required by some

     synchronous mainframes and does not apply to
     asynchronous calls.

     &R1  The modem ignores RTS.  This setting is required
          if your computer or terminal or software does not
          support RTS.

     &R2  Hardware flow control of received data enabled.
          Default.  The modem sends data to the computer or
          terminal only on receipt of the RTS signal.

Software Control (&In)
----------------------
     WARNING:  In ordinary operation, the only characters
     the modem recognizes during a call are the three pluses
     (+++) of the escape code.  But when software flow
     control is enabled, the modem also looks for <Ctrl>-S
     or <Ctrl>-Q characters.  If these characters occur in a
     file or as part of a protocol, the modem reads them as
     XON/XOFF characters and acts on them.  In some cases,
     the modem drops them from the data stream.

     &I0  Disables XON/XOFF flow control of received data.
          Default.  Recommended for non-ARQ (Normal mode)
          calls, but see &I5.  The I0 option provides
          transparency for all characters except the escape
          code sequence (+++), because at this setting the
          modem does not look for control characters.

          NOTE:  Because of the risk described in the above
          warning, the settings that follow are only
          recommended for users whose data does not include
          XON/XOFF control characters.

     &I1  The Courier acts on your typed XON/XOFF commands,
          Ctrl-S or Ctrl-Q, and passes them to the remote
          computer.  Use in ARQ mode only, but keep in mind
          that the XON/XOFF characters sent to the remote
          computer may interfere with XON/XOFF signaling
          between the remote computer and remote modem.  See
          &I2.

     &I2  The Courier acts on your XON/XOFF commands, but
          removes them from the data stream instead of
          passing them to the remote computer.  This ensures
          that the remote computer does not confuse your
          XON/XOFF characters with those from its attached
          modem.  This is the recommended setting for ARQ
          mode.

          However, if the call is not in ARQ mode, there is
          no flow control on the phone link.  If you send an
          XOFF to your modem and it stops passing data, it
          has no way to tell the remote computer and modem
          to stop sending for a while, and your modem's

          buffer may overflow.  For more reliable control in
          non-ARQ mode, see &I5.

     &I3  Hewlett Packard--Host mode. Applies only to modems
          attached to an HP mainframe that uses the ENQ/ACK
          protocol.  Use in ARQ mode only.  See Appendix F.

     &I4  Hewlett Packard--Terminal mode.  Applies only to
          modems attached to terminals in an HP system that
          uses the ENQ/ACK protocol.  Use in ARQ mode only.
          See Appendix F.

     &I5  This setting is designed to enable flow control on
          the phone link when the connection is not under
          error control.  For this to work for you, the
          remote modem must have &I5 capability.

          In ARQ mode, a Courier set to &I5 operates the
          same as it does when set to &I2.  It acts on your
          XON/XOFF commands, but does not pass them to the
          remote system.  The error control protocol enables
          the modems to control the flow of data on the
          phone link.

          In non-ARQ mode, a Courier set to &I5 operates as
          though flow control were disabled (&I0):  it does
          not look for your typed XON/XOFF commands.
          However, it looks for XON/XOFF characters coming
          in over the phone link.  When the remote operator
          sends XON/XOFF commands, the Courier either
          resumes or stops transmitting data over the link
          and drops the characters from the data stream.

          If both modems are set to &I5, operators at each
          end can signal the remote modem to stop sending,
          thereby controlling the data flow on the phone
          link and preventing their own modem's buffer from
          overflowing.  At the computer or terminal/modem
          interfaces, the modems independently control the
          flow of data through their Transmit Data (&H)
          settings.

Guidelines
     Use of software flow control may prove satisfactory if
     you're only transferring text files.  However, if
     you're transferring non-text (binary) files, or using
     an Xmodem-type protocol, disable flow control entirely
     (&R1, &I0).  In addition, set the modem to &B0 and &N0,
     so that the serial port and connection rates are equal.



S-REGISTERS
------------------------------------------------------------

     The S-Registers are used to set various timing
     parameters, redefine selected ASCII characters, and
     other configuration options.  A detailed summary of the
     S-register functions is in Appendix B.  A less detailed
     summary is in the Quick-Reference card.

Sr=n Set S-Register value:  r is any S-Register; n must be a
     decimal number between 0 and 255.

Sr.b=n Alternative command for setting bit-mapped registers:
     r is the bit-mapped register; .b is the bit; n is 0
     (off) or 1 (on).

Sr?  Query contents of register r.

INQUIRY AND HELP
------------------------------------------------------------

     The modem displays information such as the current
     modem settings, product code, and call duration.  It
     also displays summary information for every command
     that the modem supports.

     For more information on Inquiry and Help commands,
     including sample displays, see Chapter 5.

TESTING
------------------------------------------------------------

     The modem can perform a number of tests including,
     Analog Loopback, Digital Loopback, and Remote Digital
     Loopback.  These tests can be used to check the
     operations of the modem's transmitter and receiver, or
     to locate a problem with a remote modem or telephone
     channel.  Error control must be disabled for these
     tests.

     See Appendix G for more information.

INTERNATIONAL CALLS
------------------------------------------------------------

     There are three commands that apply to international
     calls above 1200 bps--Bn, &Gn, &Pn.  Bn is described
     earlier in this chapter.

&Gn  This setting applies only to overseas calls at 2400 or
     1200 bps.  British phone switching systems require the
     modem to send an 1800 Hz guard tone after it sends an
     answer tone.  Some other European phone networks

     require a 550 Hz guard tone.  Guard tones are not used
     in the United States or Canada.

     &G0  No guard tone.  This is used in the U.S. and in
          Canada (Default).

     &G1  This sets a 550 Hz guard tone, and is used in
          some European countries.

     &G2  This sets an 1800 Hz guard tone, and is used in
          the U.K., and some Commonwealth countries.  &G2
          requires the B0 setting.

&Pn  This command sets the ratio of the off-hook/on-hook
     (make/break) interval for pulse dialing.  The default
     sets the modem for use in North America.  The ratio
     must be changed if the modem is used in the United
     Kingdom and some Commonwealth countries.

     &P0  Make/break ratio, U.S./Canada:  39%/61%.  Default.

     &P1  Make/break ratio, United Kingdom, some
          Commonwealth countries:  33%/67%.

MISCELLANEOUS COMMANDS
------------------------------------------------------------

Cn   Transmitter enabled/disabled.

     C0   Transmitter disabled; receive-only condition.

     C1   Transmitter enabled (Default).

Kn   Modem clock operation:  Call-duration or Real-time
     mode.  Displayed with ATI3 and ATI6 commands.

     K0   Display current call-duration if online.  Display
          last call-duration if offline.  Default.

     K1   Return actual time at ATI3.  Clock is set using
          ATI3=HH:MM:SS K1.

&Yn  Break handling.  This command allows you to send a
     break to abort data transfer without disconnecting from
     the phone link.

     &Y0  Destructive, don't send Break.

     &Y1  Destructive, expedited (Default).

     &Y2  Nondestructive, expedited.

     &Y3  Nondestructive, unexpedited; modem sends Break in

          sequence with data received from computer or
          terminal.

     NOTE:  If the call is under MNP5 data compression,
     destructive Breaks cause both modems to reset their
     data compression tables.  When transmission resumes,
     the modems build new tables, and the result is lower
     than normal throughput.

&ZC=s Write the following command string s to NVRAM.
     The command string may be up to 30 characters long;
     spaces are not counted.  This command can be used so
     that you can call another modem without loading your
     communications software.

     After storing a command, you can program the voice/data
     switch to execute the stored command string when
     pressed.  The following example assigns a command

     string that displays the link diagnostics screen when
     you press the voice/data switch.
               AT&ZC=I6 <Enter>

     The function of the voice/data switch is determined by
     the setting of Register S32, as described in Appendix
     F.  Set the voice/data switch function to execute
     stored command string by setting Register S32 to 9 with
     the following command.
               ATS32=9 <Enter>

     Note that you can reset the voice/data switch at any
     time to one of the other available functions.
     Additionally, you can overwrite the stored command
     string with a new one at any time.

     Once you've stored your command string and set Register
     S32, all you need to do is press the voice/data switch
     whenever you want the command string executed.

&ZC? Display the stored command string.

%T   Enables the modem, when off hook, to detect the tone
     frequencies of dialing modems.  %T is meant primarily
     for use with network applications, but may also be
     integrated into certain software programs.  For
     example, %T could be used in a security program to
     identify incoming tone security codes.

     To enable %T, type ATH1 <Enter> to force the modem off
     hook.  Then type AT%T <Enter>.

     To return the modem to Command mode, press any key or
     drop the computer's or terminal's DTR signal.  The
     modem responds OK.
+----------------------------------------------------------+
|                                                          |
|   CHAPTER 4.  FAX OPERATIONS AND CALL SELECTION          |
|                                                          |
+----------------------------------------------------------+

------------------------------------------------------------
Fax Operations
------------------------------------------------------------


COMPATIBILITY
------------------------------------------------------------

The Courier modem provides Group III-compatibility when
combined with Class 1 or Class 2.0 fax software.  In
addition, the modem adheres to the following standards.

NOTE:  The International Telecommunication Union (ITU-T) was
formerly the International Telegraph and Telephone Consul-
tative Committee (CCITT).

TIA/EIA-578    Service Class 1 Asynchronous Facsimile DCE
               Control Standard
TIA/EIA-592    Service Class 2.0 Asynchronous Facsimile DCE
               Control Standard
ITU-T V.17     14.4K/12K bps
ITU-T V.29     9600/7200 bps
ITU-T V.27 ter 4800/2400 bps
ITU-T V.21     300 bps

Fax Modem Guidelines
--------------------
Fax operations require facsimile-compatible software that
can send or receive Group III faxes.  Follow the
instructions in your fax software manual.

The modem's normal operating mode is Data mode.  If your fax
software is typical, it automatically switches the modem to
Fax mode when you run the program, and resets the modem to
Data mode when you exit the program.

If you have a problem, however, and think the modem may be
in the wrong mode, you can use one of the following AT
commands to manually switch the modem:

        AT+FCLASS=0 (Switch to Data mode) <Enter>
        AT+FCLASS=1 (Switch to Class 1 Fax mode) <Enter>
        AT+FCLASS=2.0 (Switch to Class 2.0 Fax mode) <Enter>

If you are not sure whether the modem is in Data or Fax
mode, type the following command.
          AT+FCLASS? <Enter>

The modem  returns a value of 0 to indicate Data mode,  1 to
indicate Class 1 Fax mode, or 2.0 to indicate Class 2.0 Fax
mode.
NOTE:  Whenever the fax modem is reset using the ATZ
command, by toggling the DTR signal, or by turning the power
off and on, the modem will be set to Data mode.

Fax Mode Flow Control Setting
-----------------------------
Many facsimile software products use software flow control
when the modem is in Fax mode.  Throughout our
documentation, we recommend use hardware flow control for
Data mode (factory setting).  However, to allow
compatibility with software products that use software flow
control by default, U.S. Robotics fax modems now
automatically change to software flow control when entering
Fax mode.

FCC Notice
----------
FCC part 68, rules regarding fax operation, has been amended
as follows:

Telephone facsimile machines--identification of the sender 
of
the message:  It shall be unlawful for any person within the
United States to use a computer or other electronic device
to send any message via a telephone facsimile machine unless
such a message clearly contains, in a margin at the top or
bottom of each transmitted page or on the first page of the
transmission, the date and time it is sent and an
identification of the business, other entity, or individual
sending the message and the telephone number of the sending
machine or of such business, other entity, or individual.
Telephone facsimile machines manufactured on and after
December 20, 1992 must clearly mark such identifying
information on each transmitted page.

NOTES TO PROGRAMMERS
------------------------------------------------------------

Lists of supported Class 1 fax commands and optional Class
2.0 commands are in the Technical Specifications in this
manual, Appendix I.

If you want to know more about the supported Class 1 fax
commands, refer to the standard for the Service Class 1 fax
protocol.

     ANSI/EIA/TIA-578-1990 (EIA-578)
     Asynchronous Facsimile DCE Control Standard
     November, 1990   Approved:  October 22, 1990






For more information on Class 2.0, refer to the standard for
the Service Class 2.0 fax protocol.

     ANSI/EIA/TIA-592-1993 (EIA-592)
     Asynchronous Facsimile DCE Control Standard
     May, 1993

You can obtain copies of these standards by contacting
Global Engineering Documents, at 1-800-854-7179.

------------------------------------------------------------
CALL SELECTION
------------------------------------------------------------
Courier High Speed modems now support Call Selection, which
is a method of reporting whether an incoming call is Data,
Fax Class 1, or Fax Class 2.0.  It is especially useful for
Bulletin Board systems, as it automates recognition of
different calls from multiple users.

Call Selection is an optional Service Class 2.0 feature, and
is also implemented by U.S. Robotics for Fax Class 1
applications.

To obtain a copy of the technical specification of U.S.
Robotics' implementation of Call Selection for Fax Class 1,
call our BBS at (708) 982-5092 and download the file
CALLSEL.TXT.

For information on implementing Fax Class 2.0 Call
Selection, see the standard listed above.  For a list of the
optional Fax Class 2.0 commands supported by U.S. Robotics,
see the Technical Specifications in Appendix H.



















+----------------------------------------------------------+
|                                                          |
|   CHAPTER 5.  QUERIES AND HELP SCREENS                   |
|                                                          |
+----------------------------------------------------------+

USER INQUIRIES (In)
------------------------------------------------------------
The Inquiry command has 9 options.  The most commonly used
options display the following information:

     ATI3      Call duration
     ATI4      Current settings
     ATI5      NVRAM settings
     ATI6 Link diagnostics summary

I0   The modem returns a 4-digit product code.  If you have
     a problem and call U.S. Robotics' Technical Support
     Department, you may be asked for this product code.

I1   The modem performs a checksum of its read-only memory
     (ROM) and returns the result to the screen.  This
     function is used only in factory testing.  The modem
     should always read the same number.

I2   The modem performs a test of its random access memory
     (RAM) and returns either the OK (0) or ERROR (4) result
     code, followed by OK when the test is completed.  You
     may want to use this command as a checkpoint if the
     modem appears to be malfunctioning.

I3   The modem returns the duration of the last call if set
     to K0.  It displays the actual time if set to K1.  See
     the description of the Kn command in Chapter 3.

I4   The modem displays its current configuration.

I5   The modem displays the configuration stored in
     nonvolatile random access memory (NVRAM).  If your
     modem connects to a modem that has Dial Security and
     local access enabled, you cannot view the stored phone
     numbers.

I6   During a connection, the modem monitors and stores
     information about link operations.  When the call is
     ended, you can request a diagnostic summary, as in the
     following example.  The duration of the last call or
     real time is displayed depending on the Kn setting.

For calls under data compression, the number of
characters sent may be less than the number of octets
sent, due to buffering operations.  Line Reversals only
apply to HST-mode operations, when the modems switch
the high and low speed channels.  At this time, online
fallback is only reported Enabled in HST-mode.
Many terms used in the display are self-explanatory
except for the following:

     Octets:  Compressed data units.  If the number of
     octets is greater than the number of characters sent,
     the modems probably used MNP5 compression on an already
     compressed file, and the result was expanded data.

     Line Reversals:  The number of times HST-mode modems
     switched the high and low speed channels.

     Blers:  Errors in data and protocol blocks.  If there
     were many block errors, your receiver may have
     experienced problems on the line.

     Blocks Resent:  These represent blocks the remote modem
     resent due to the previous category, Blers.

     Link Timeouts:  Protocol detection problems:
     communications were severed momentarily, and the modems
     probably recovered.  This does not indicate the retry
     timeout.

     Link Naks:  Negative acknowledgments (one or more
     blocks).

     Data Compression:  Indicates the type of data compres-
     sion negotiated for the call (V42BIS or MNP5) or NONE.
     A V42BIS response includes the size of the dictionary
     and the maximum string length used, for example,
     2048/32.  See Appendix A for more information.

     Equalization Long/Short:  Status of S15 bit 0; long if
     bit 0=0, short if bit 0=1.  Short equalization applies
     only to HST modems.

     Fallback:  Enabled/Disabled:  indicates whether or not
     the modems negotiated online fallback during the
     connection sequence.

     Protocol:  Indicates the error control protocol
     negotiated (LAPM, HST, MNP, NONE).

     Speed:  The last rates at which the
     receiver/transmitter were operating before
     disconnecting.







     Disconnect Reason:  Possible reasons the modem hung up
     are as follows:

          DTR dropped:  The computer dropped the Data
          Terminal Ready signal, terminating the call.

          Escape code:  The operator sent the modem the +++
          escape code.

          Loss of carrier:  The modem detected loss of the
          remote modem's carrier and waited the duration
          specified in Register S10 (default is 0.7
          seconds).

          Inactivity timeout:  The modem detected no
          activity on the line for the duration specified in
          Register S19 (default is 0, timer disabled).

          MNP incompatibility:  The modem is set to &M5 and
          the remote modem does not have MNP capability, or
          there was an MNP negotiation procedure error.

          Retransmit limit:  The modems reached the maximum
          of twelve attempts to transfer a data frame
          without error.

          LD received:  The remote modem sent an MNP error
          control Link Disconnect request.

          DISC:  The remote modem sent a V.42 Disconnect
          frame.

          Loop loss disconnect:  The modem detected a loss
          of current on the loop connecting it with the
          telephone company central office.  This usually
          occurs because the remote modem has hung up:  the
          central office drops current momentarily when
          there is a disconnect at the other end of a call.
          Unless Register S38 is set higher than zero, the
          modem immediately hangs up at loop loss.

          Unable to Retrain:  After several attempts,
          disturbances on the phone line prevented the 
          modems from retraining, and they could no longer
          transmit or receive data.

          Invalid speed:  The modem is set to &N1 or higher,
          for a fixed link rate, and the remote modem is not
          operating at the same rate.

          XID Timeout:  The modems failed to negotiate the
          V.42 Detection (XID Exchange) phase.
          SABME Timeout (Set Asynchronous Balance Mode

          Extended):  The modems failed this part of V.42
          link negotiation.

          Break Timeout:  Incompatible processing of a Break
          signal occurred.

          Invalid Codeword:  The modem received an invalid
          V.42 bis (compression) frame.

          A Rootless Tree:  The modem received an invalid
          V.42 bis (compression) frame.

          Illegal Command Code:  The modem received an
          invalid V.42 bis (compression) frame.

          Extra Stepup:  The modem received an invalid V.42
          bis (compression) frame.

     Dial Security Disconnect Reason:  Possible reasons the
     answering modem may have hung up during a Dial Security
     session are as follows:

          Security Abort:  The modem hung up because it
          received an invalid password three times.

          Prompting Not Enabled:  The modem hung up because
          the originating modem did not send an autopass
          password, and prompting wasn't enabled.

          Non-ARQ Mode:  The modem hung up because the
          originating modem was set for error control and
          the answering modem was set for non-error control.

          No Prompting in Non-ARQ:  Prompting was enabled,
          but the modem hung up because the originating
          modem was set for error control, and the answering
          modem was set for non-error control.  The
          answering modem cannot prompt when it is set for  
          non-error control.

I7   The modem returns a product configuration.  If you have
     a problem and call U.S. Robotics' Technical Support
     staff, you may be asked to read this screen.

I10  View Dial Security Account status.  For security
     administrators only, unless local security is disabled,
     S53=0 or S53.2=0.

S-REGISTER QUERY (Sr?)
------------------------------------------------------------

This command allows you to view the contents of a particular
S-Register, as in the following example that requests the

contents of Register S0 ("On what ring will the modem
answer?"):
          ATS0? <Enter>

PHONE NUMBER QUERY (&Zn?)
------------------------------------------------------------

At this command, the modem returns the phone number stored
in NVRAM at position n, as in the following example that
includes a sample modem response:
          AT&Z3? <Enter>
          5551234

LAST-DIALED NUMBER QUERY (DL?)
------------------------------------------------------------

At this command the modem displays the number stored in the
last-dialed number buffer:
          ATDL? <Enter>

STORED COMMAND STRING QUERY (&ZC?)
------------------------------------------------------------

At this command the modem displays the command string stored
in NVRAM with the &ZC=s command:
          AT&ZC? <Enter>

HELP SCREENS
------------------------------------------------------------

Courier modems provide five Help screens:  summaries of the
basic AT command set, extended ampersand (&) command set,
Dial command options, S-Register functions, and percent (%)
command set.

Stop/Restart Display
--------------------
The following command stops the display. Hold down the
Control key and type "S":
          <Ctrl>-S

To restart the display, use the same command or press any
key.

Cancel Display
--------------
Either of the following commands cancels the display.
          <Ctrl>-C
          <Ctrl>-K





Basic Command Set ($)
---------------------

At AT$, the Courier displays a screen that shows a partial
summary of the command set.  A second screen, activated by
pressing any key, shows the remaining commands.

Extended Command Set (&$)
-------------------------

At AT&$, the Courier displays a screen that shows a partial
summary of the extended ampersand command set.  A second
screen, activated by pressing any key, shows the remaining
command set.

Dialing (D$)
------------

At ATD$, the Courier displays this Dial command summary.

S-Register Functions (S$)
-------------------------

At ATS$, the Courier displays a screen that shows a partial
summary of the S-Register functions.  A second screen,
activated by pressing any key, shows the remaining
registers.

Percent Commands (%$)
---------------------

At AT%$, the Courier displays a screen that shows a partial
summary of the percent command functions.  A second screen,
activated by pressing any key, shows the remaining
registers.



















+----------------------------------------------------------+
|                                                          |
|   APPENDIX A.  LINK NEGOTIATION (HANDSHAKING) AND        |
|                HANDSHAKING                               |
|                                                          |
+----------------------------------------------------------+


      This appendix includes detailed information on how
      U.S. Robotics modems in HST and V.32 terbo mode
      negotiate with remote modems for the rate and other
      characteristics of each connection.  You may find it
      helpful if you are having difficulty connecting with
      another modem.

      In addition, you'll find information on error control
      and, especially useful, some statistics and guidelines
      on using the modem for the best throughput.

      The following text relies on familiarity with  the
      term ARQ.  ARQ (automatic repeat request) designates a
      connection under error control.

LINK NEGOTIATION (HANDSHAKING)
------------------------------------------------------------

      During high-speed link negotiation, timing and
      procedures differ for HST or V.32 terbo modulation, as
      follows.

HST-mode
--------
      Serial port rate:  115.2K/57.6K/38.4K/19.2K/9600 bps
      (115.2K, 57.6K, or 38.4K required for 16.8K or 115.2K,
      57.6K, 38.4K, or 19.2K for 14.4K connections)

      Modem settings:  B1, &B1, &H1/&H2/&H3, &M4/&M5, &N0

      1. The modems begin handshaking by training
      (synchronizing) at 2400 bps and exchanging information
      on their error control, data compression, and speed
      capabilities.

      2. Once the modems enable error control, handshaking
      proceeds as follows.  If the remote modem is operating
      at 2400 bps or lower, the Courier stays at 2400 bps or
      falls back to match the remote modem's slower rate.

      If the remote modem is HST-compatible and operating at
      a higher speed, both modems shift up and train at 9600
      bps.  From there, depending on the speed of the remote
      modem, they shift up again to 12K bps, 14.4K bps, and
      again to 16.8K bps; or they fall back to 7200 bps and

      again to 4800 bps, if the remote modem is operating at
      one of those lower speeds.

      Initially, the high-speed channel is allocated to the
      answering modem, the 450-bps channel to the calling
      modem.  This allocation reverses if the calling modem
      has more data to transmit than the answering modem.

Specialized High-Speed Connection
---------------------------------
      It's possible for two modems in HST-mode to connect
      directly at 9600, 12K, 14.4K or 16.8K bps, without
      2400 bps handshaking.  However, this is only
      recommended for faster connections in specialized
      installations where the computer and software manage
      error control.  The reason is that there can be no
      error control because HST modems negotiate error
      control during 2400 bps handshaking.

      Both modems must be set as follows.  High speed
      handshaking requires a fixed connection rate:  the
      modem only connects if the remote modem is operating
      at the same connection rate--9600 (&N6), 12K (&N7),
      14.4K bps (&N8), or 16.8K bps (&N9).

      Serial port rate:  115.2K/57.6K/38.4K/19.2K/9600 bps
      (57.6K, 38.4K, or 19.2K required for 16.8K or 14.4K
      connections) 

      Modem settings:  B1, &B1, &H1/&H2/&H3, &M0,
      &N6/&N7/&N8/&N9

HST-mode, Error Control Disabled
--------------------------------
      If error control is disabled--that is, the Courier HST
      is set to &M0 or the remote modem isn't set for error
      control and the Courier HST reverts to &M0--the 
Courier
      operates in one of the following ways.

      1. If set to &N0, it only connects at 2400 bps or
      lower.  This ensures that there will not be data
      transfer at high speeds unless the call is protected
      by error control.

      Courier HST modems negotiate error control during 2400
      bps handshaking.  If they cannot connect under error
      control, they stay at 2400 bps.  Or, if the remote
      modem is operating at a lower rate, the Courier HST
      switches to the lower rate.

      2. If set to &N6, &N7, &N8 or &N9, the Courier will
      handshake at the higher speed, 9600, 12K, 14.4K or
      16.8K bps, as shown in the previous configuration
      example, Specialized High-Speed Connection.  However,
      that configuration example should only be used in the

      special situation described, where the system takes
      care of error control.

      NOTE:  Without error control, there are no high speed
      line reversals.  The high speed channel is always
      allocated to the answering modem.  Also, there is no
      online fallback to protect the connection on impaired
      lines.

V.32 terbo mode
---------------

      The V.32 terbo handshaking described in this section
      is proprietary to U.S. Robotics, and allows two V.32
      terbo modems to connect at 21.6K and 19.2K bps.  In
      addition, U.S. Robotics V.32 terbo modems, when
      connecting with each other, use an enhanced
      proprietary handshaking procedure which allows them to
      connect faster and to retrain faster during calls. 
      They must, however, establish a V.42 error control
      connection.  This proprietary handshaking is described
      after the next section, under U.S. Robotics V.32 terbo
      to U.S. Robotics V.32 terbo.

V.32 terbo
-------------
      NOTE:  High speed calls are highly vulnerable to
      errors unless the data is protected by error control. 
      The operations described below take place even if
      one of the modems is not set for error control,
      thereby prohibiting error control for the call.

      Serial port rate:  115.2K/57.6K/38.4K/19.2K bps

      Modem settings:  B0, &B1, &H1/&H2/&H3, &M4/&M5, &N0
      
      WARNING:  If the calling modem dials in at 19.2K,
      16.8K, 14.4K or 12K bps (for 19.2K, 16.8K, or 14.4K
      bps connections), answering V.32 terbo modems shift
      their serial port rate up to 19.2K bps, and send
      information to the computer at 19.2K bps.  If your
      computer is limited to a rate of 9600 bps, disable
      high-speed modulation by setting Register S34 to a
      value of 3 (ATS34=3).  The calling modem will then
      shift down to 9600 bps for a V.32, not V.32 terbo,
      connection.
      

      1. The answering modem first sends out a 2100 Hz
      answer tone identifying it as a V.32 or V.32 terbo
      modem.  If the calling modem recognizes the tone, the
      modems connect at the highest possible speed, 19.2K or
      16.8K bps.  If the  calling modem is a V.32 modem, its

      maximum speed is 9600 bps, and the modems may connect
      at that rate.  But see paragraph 3.

      2. If the calling modem doesn't recognize the answer
      tone, the answering modem then sends a 2250 Hz answer
      tone used by 2400, 1200 or 300 bps modems.  If the
      calling modem is operating at one of those rates, the
      modems connect at the calling modem's rate.

      3. If the modems don't connect as in paragraph 1 or 2,
      the answering V.32 terbo modem then sends extra V.32
      answer tones.  If the calling modem is a V.32 modem,
      the answering V.32 terbo modem shifts its speed down
      to 9600 bps and the modems connect at that speed. 
      This extended V.32 handshaking ensures connections
      with V.32 modems if they did not connect as in
      paragraph 1.

      It may even be necessary to extend the length of these
      tones if the modem is to answer older, "dumb" V.32
      modems.  Register S28 is used to modify the duration
      of these extra V.32 tones.  See S28 in Appendix B.

U.S. Robotics V.32 terbo to U.S. Robotics V.32 terbo
----------------------------------------------------

      1. The modems first negotiate a V.42 error control
      connection.  Speed negotiation is part of the V.42
      detection/LAPM sequence.  If they fail to make a
      V.42 connection, these modems follow the procedures
      described under V.32 terbo, above.

      2. The Receiver of each modem dictates its modem's
      highest speed, with negotiation beginning at 7200 bps
      and proceeding upward to the 21.6K bps maximum.  This
      means that your modem's receiver may be operating at a
      different speed from your modem's transmitter, which
      operates at the same rate as the remote modem's
      receiver.  In other words, the rate at your modem's
      Originate frequency may be different from the rate at
      your modem's Answer frequency.

      Because of this asymmetrical design, one frequency may
      suffer line hits or other impairments, and fall back
      to a slower speed, while the other does not.  The
      result is more efficient line operation.  If the
      impairments are severe, the modems use normal
      retraining.

      NOTE:  Answering V.32 terbo modems shift their serial
      port rate up to 38.4K (for 21.6K connections) if the
      calling V.32 terbo modem dials in at 21.6K.
      The answering V.32 terbo modem then sends data to its
      computer at 38.4K bps.

Dual Standard Handshaking
-------------------------

      Dual Standard modems always connect with each other,
      either in HST-mode or in V.32 terbo mode.  However, we 
      recommend that Dual Standard modems be set to B0 and
      to &N0, so that they can connect with V.32 terbo, HST
      and lower-speed modems, in both Originate and Answer
      modes.

      A Dual Standard modem set to B1 (HST) does not send
      out any V.32 terbo or V.32 answer tones, and therefore
      cannot answer calls in those modes.  A Dual Standard
      modem set to B0 will switch to HST-mode for that call
      only if the other modem is operating in HST-mode.

ERROR CONTROL AND THROUGHPUT
------------------------------------------------------------

Overview
--------
      Error control is available for calls at 1200 bps and
      above.  It can be disabled, although high speed calls
      (above 2400 bps) should always be under error control.
      The operations defined in an error control protocol
      include the following:

         #  Establishment of compatibility
         #  Data frame formatting
         #  Error detection through Cyclic Redundancy
               Checking (CRC)
         #  Retransmission of corrupt data frames

      The Courier is set at the factory to &M4, causing it
      to try for an error control connection and, if that
      isn't possible, to proceed with the call in Normal
      mode.  The modem first tries for a V.42 connection,
      then an MNP connection.  The following information is
      based on the Courier's setting of &M4.

V.42 Handshaking
----------------
      This international standard includes a two-stage
      handshaking process:

         #  A Detection phase that is based on an exchange
            of predefined characters.
         #  LAPM (Link Access Procedures for Modems)
            Negotiation.  In this phase, the modems identify
            their capabilities concerning maximum data block

            size and the number of outstanding data blocks
            allowed before an acknowledgment is required.

MNP Handshaking
---------------
      This protocol is supported by the ITU-T V.42
      Recommendation.  It was originally developed by
      Microcom, Inc. and is now in the public domain.

      MNP is based on special protocol frames.  If the
      remote modem doesn't recognize an MNP Link Request,
      error control isn't possible. (In HST asymmetrical
      mode, U.S. Robotics modems use a proprietary scheme
      similar to MNP.)

Data Compression
----------------
      If the modems successfully establish a V.42
      connection, they also negotiate for V.42 bis data
      compression.  If they successfully establish an MNP
      connection, they negotiate for MNP5 data compression. 
      The type of compression for a call, if any, is
      reported in the ATI6 display, and in the CONNECT
      message if the modem is set to &A3.

      Modems using V.42 bis compression negotiate the
      following options and report them in the ATI6 display.

         #  Dictionary size, that is, the amount of memory
            available for compression table entries. 
            (Entries are codes devised for redundant data. 
            The data is packed into shorter data units,
            called code words, and unpacked by the receiving
            modem.)

           Possible sizes are as follows.  U.S. Robotics
           modems use 11-bit, or 2048- entry dictionaries,
           but drop down if the remote modem uses a 512- or
           1024- entry dictionary.  The size of the
           dictionary for a call is reported in the ATI6
           display.

           Bits      Entries
           -----     -------
           9         512
           10        1024
           11        2048

         #  Maximum string length of each entry.  As the
            dictionary fills, the modem deletes the oldest
            unused strings.

      V.42 bis compression is more efficient than MNP5
      compression in part because it dynamically deletes
      entries that are no longer used.  In addition, it
      works better with files that are already compressed. 
      These include .ZIP files down-loaded from many
      Bulletin Boards and 8-bit binary files, which seem to
      the modem to be compressed.

      MNP5 compression should not be used with such files
      because it adds data to them, which lessens
      throughput.  (The additional data is stripped when the
      file is decompressed by the remote modem.)  When
      transferring such files, it's best to set the modem to
      &K3:  this allows V.42 bis compression to work
      dynamically with the compressed data, but disables
      MNP5.

Flow Control
------------

Flow control of data from the computer is required under 
error control for two reasons:

      1. The transmitting modem buffers a copy of each frame
      it transmits to the remote end until it is
      acknowledged by the receiving modem.

      2. If errors are encountered, retransmission activity
      can cause a steady stream of data from the computer to
      overflow the buffer.


Throughput Guidelines
---------------------

      The following guidelines should help to make the most
      of the modem's advanced performance features.  In many
      instances, experimentation and experience will
      indicate what works best for your applications.

      1. Optimal throughput is attained under the following
         conditions:

        #  The communications software allows fixing the
           serial port rate higher than the connection rate,
           by setting the software to 115.2K, 57.6K, or
           38.4K bps and setting the modem to &B1.

           If the software automatically switches serial 
           port rates to follow the connection rate, the
           modem's serial port rate must be also set to
           follow the connection rate for each call, &B0,
           and throughput will be limited.

           Installations with specialized software may want
           to enable a fixed serial port rate for ARQ calls
           and a variable serial port rate for non-ARQ 
           calls.  See the &B2 command in Chapter 3.

        #  The call is under data compression.
        #  The data is comprised of text files rather than
           binary files such as .EXE or .COM files.  See the
           table at the end of this appendix.

      2. MNP5 compression is disabled for files that are
         already compressed and 8-bit binary files, that
         appear to the modem to be already compressed.  MNP5
         is disabled by setting the modem to &K3.

      3. The file transfer is not slowed down by a file-
         transfer protocol.  Many non-text files require a
         file transfer protocol, but the results vary.  For
         example, certain public domain file transfer
         protocols have the following effects:

         Kermit   Newer versions support packets up to 9K
                  and a sliding window design to eliminate
                  turn-around delay.  With earlier versions,
                  however, throughput may be severely
                  reduced due to short block lengths
                  (possibly under 128 bytes) and
                  acknowledgment turnaround time.

         Xmodem   Throughput may be reduced if your version
                  uses short block lengths (128 bytes). 
                  Some versions use larger blocks (1K
                  blocks).  Throughput is also reduced by
                  overhead (error control protocol
                  information).

         Ymodem   There is an improvement over Xmodem, due
                  to larger block lengths (1K bytes), but
                  throughput is still reduced by the
                  protocol's error control overhead.

         The above protocols further reduce throughput when
         an error control connection is established.  The
         accuracy of the data is checked both by the
         file transfer protocol and the modem.  To avoid
         redundancy, use the above protocols only for non-
         ARQ connections, and only at speeds of 2400 bps and
         below.

         For the best throughput, but on error-controlled
         connections only and with hardware flow control, we
         recommend the most current version of Zmodem.
         Overhead is minimal with this protocol, with
         throughput almost equal to that obtained with no
         file-transfer protocol.  Zmodem should also be used
         for non-ARQ connections.  Leave the modem at its
         &M4 and &K1 settings for both error control and
         data compression.  Ymodem-G is another good choice,
         but never without both the local and remote modems
         using error control:  if Ymodem-G detects an error,
         it aborts the transfer.  Do not use either protocol
         with software flow control (XON/XOFF signaling).

Achievable Throughput
---------------------

      The tables on the next page indicate the typical
      throughput, in characters per second (cps), that can
      normally be expected under the following conditions.
        #  Connection (link) rates of 14.4K, 16.8K, 19.2K
              and 21.6K bps
        #  Serial port rate set at 57.6K bps; modem set to
              &B1
        #  V.42 bis compression negotiated for the call, and
              the default size 11-bit, 2048-entry dictionary
        #  Straight data (not already compressed, no file-
              transfer protocol)
        #  Transmission from a fast (486) computer

      NOTE:  .ZIP files are already compressed or appear to
      the modem to be compressed.  Additional MNP5
      compression causes throughput lower than what can be
      expected using MNP without compression.  We recommend
      setting the modem to &K3 when transferring these
      files, to allow V.42 bis but disable MNP5.

                    Throughput (cps) when set to 14.4K bps
      File Type                         MNP5      V.42 bis
      ----------------------------------------------------
      Assembler or Compiler listing     2880      3840 
      Text file                         2325      3400
      Binary file: .EXE                 2175      2030
      .ZIP files (common on BBS's)      1500      1700


                      Throughput (cps) when set to 16.8K bps
      File Type                         MNP5      V.42 bis
      ----------------------------------------------------
      Assembler or Compiler listing     3360      4480 
      Text file                         2713      3967
      Binary file: .EXE                 2538      2368
      .ZIP files (common on BBS's)      1750      1983








                      Throughput (cps) when set to 19.2K bps
      File Type                         MNP5      V.42 bis
      ----------------------------------------------------
      Assember or Compiler listing      3840      5120
      Text file                         3100      4533
      Binary file: .EXE                 2900      2706
      .ZIP files (common on BBS's)      2000      2266


                      Throughput (cps) when set to 21.6K bps
      File Type                         MNP5      V.42 bis
      ----------------------------------------------------
      Assember or Compiler listing      4320      5760
      Text file                         3487      5100
      Binary file: .EXE                 3263      3045
      .ZIP files (common on BBS's)      2250      2550






































+----------------------------------------------------------+
|                                                          |
|   APPENDIX B.  SUMMARIES AND TABLES                      |
|                                                          |
+----------------------------------------------------------+


CONTENTS
------------------------------------------------------------

          DIP Switch Summary
          Default Settings
          S-Register Summary









































DIP SWITCH SUMMARY
------------------------------------------------------------

PURPOSE
-------
The DIP switches, located at the rear of the modem, are for
adapting the modem to your equipment and personal require-
ments.  The STOP guide that comes with the modem indicates
the recommended switch settings for many communications
software packages.  If necessary, review your software
documentation.

Some users are able to move a single switch with a finger
tip.  If this doesn't work for you, use a toothpick or other
small instrument.  Do not use a lead pencil.

OPERATIONS
----------
The DIP switch settings are power-on defaults, read by the
Courier when it is turned on.  If changed when the modem is
on, switches 1-7, and 9 require the ATZ (software reset)
command to initiate the new settings.  If you've set switch
8 OFF to disable command recognition, and want to return the
modem to Smart mode so that it responds to commands, just
reset switch 8 to ON.
When you issue the ATZ command, the modem reads its DIP
switch settings and resets either to its defaults (DIP
switch 10 OFF) or factory settings (DIP switch 10 ON).

			Table B.1--DIP Switches

               Factory
     Switch    Setting        Function                      
     -------------------------------------------------------
          1    OFF       Data Terminal Ready Operations
                             OFF  Normal DTR operations:   
                                  computer must provide DTR
                                  signal for modem to accept
                                  commands; dropping DTR
                                  terminates a call
                             ON   DTR always ON (Override)

          2    OFF            Verbal/Numeric Result Codes
                              OFF  Verbal (word) results
                              ON   Numeric results

          3    ON             Result Code Display
                              OFF  Results suppressed
                              ON   Results enabled

          4    OFF            Command Mode Local Echo
                              OFF  Keyboard commands   
                                   displayed
                              ON   Echo suppressed
               Factory
      Switch   Setting        Function                      
      ------------------------------------------------------

          5    ON             Auto Answer
                              OFF  Modem answers on first
                                   ring
                              ON   Auto answer disabled

          6    OFF            Carrier Detect Operations
                              OFF  Courier sends CD signal
                                   when it connects with
                                   another modem, drops CD
                                   on disconnect
                              ON   CD always ON (Override)

          7    OFF            Auxiliary, DIP Switch 3 ON
                              OFF  Result codes in Originate
                                   and Answer mode
                              ON   Result codes in Answer
                                   mode disabled

          8    ON             AT Command Set Recognition
                              OFF  Command recognition      
                                   disabled (Dumb mode)
                              ON   Recognition enabled
                                   (Smart mode)

          9    OFF            Escape Code (+++) Response
                              OFF  Modem hangs up, returns
                                   to Command mode, sends NO
                                   CARRIER result
                              ON   Modem maintains
                                   connection, returns to
                                   Command mode, sends OK
                                   result

          10   OFF            Power-on and ATZ Reset
                              Software Defaults
                              OFF  Load from nonvolatile
                                   memory (NVRAM)
                              ON   Load factory settings
                                   from read only memory
                                   (ROM)










DEFAULT SETTINGS
----------------

User-programmable Defaults
--------------------------
You can create your own default configuration and store it
in nonvolatile random access memory (NVRAM) using the &W
command described in Chapter 3.  As long as DIP switch 10 is
OFF when you power on the modem, your defaults are loaded
into the modem's random access memory (RAM).  To view your
NVRAM settings at any time, use the ATI5 command.

Tables on the next several pages list the options you can
store in NVRAM, including S-Register settings.  If DIP
switch 10 is ON at power-on, the factory template 0 settings
are loaded instead.  The modem has four factory setting
templates (&F0-F3).  By default, the first time the modem is
turned on, the modem loads the settings stored in NVRAM,
which are the same as the settings in factory template 1
(&F1).

The following command example substitutes several user-
defined defaults for factory settings.  The modem also
stores the rate, word length and parity it detects from the
AT command prefix.
          AT X1 &B0 &M5 &H0 M3 &W <Enter>

The modem is shipped with DIP switch 10 OFF, so when it is
powered on it loads the settings from NVRAM.  Until these
settings are changed, they are they same as the settings
permanently stored in factory settings template 1 (&F1).
You can alter any of these settings, create your own power-
on defaults, and then save them with the &W command.  See
Chapter 3.




















Table B.2--&F1 Hardware Flow Control Default Template

NVRAM Options            Setting   Description
------------------------------------------------------------
Handshake option           B0      ITU-T answer sequence
Normal/Error control/sync  &M4     Normal/error control
Data compression           &K1     Enabled
Transmit data hardware     &H1     Hardware flow control
Rec'd data hardware
  flow control             &R2     Enabled
Rec'd data software
  flow control             &I0     Disabled
Serial port rate select    &B1     Serial port rate fixed
                                   higher than connect rate
Link rate select           &N0     Variable
Result code subset         X7      Extended.  Includes all
                                   codes except VOICE
Protocol response codes    &A3     Full protocol codes
Tone/Pulse dialing         P       Pulse dial
Online local echo          F1      Disabled
Speaker control            M1      ON during dial through
                                   connect
Remote Digital
  Loopback (RDL)           &T5     Deny RDL
Normal/Leased/
  Cellular line            &L0     Normal phone line

Data Set Ready
  operations               &S0     Override enabled
Break handling             &Y1     Clear buffer, send
                                   immediately

Stored telephone number    &Z0-9=s Blank
Pulse dial make/
break ratio                &P0     U.S./Canada
Guard tone                 &G0     U.S./Canada

Word length*               8
Parity*                    0       None
DTE rate* (Kbps)           19.2    --

*  Detected by the modem from the AT prefix of the &W com-
mand that writes your defaults to NVRAM.  Set your software
to the desired word length, parity, and serial port rate
defaults before sending the modem the AT . . . &W string.









The &F2 and &F3 factory setting templates are similar to the
&F1, with the exception of the commands have one aestrisk in 
front of them in tables B.3, B.4 and B.5.

Table B.3--&F2 Software Flow Control Template

NVRAM Options            Setting   Description
------------------------------------------------------------
Handshake option           B0      ITU-T answer sequence
Normal/error control/sync  &M4     Normal/error control
Data compression           &K1     Enabled
*Transmit data
  flow control             &H2     Software flow control
*Rec'd data hardware
  flow control             &R1     Disabled
*Rec'd data software
  flow control             &I2     Enabled

Serial port rate select    &B1     Serial port rate fixed
                                   higher than connect rate
Link rate select           &N0     Variable

Result code subset         X7      Extended.  Includes all
                                   codes except VOICE
Protocol response codes    &A3     Full protocol codes
Tone/Pulse dialing         P       Pulse dial
Online local echo          F1      Disabled
Speaker control            M1      ON during dial through
                                   connect

Remote Digital
Loopback (RDL)             &T5     Deny RDL
Normal/Leased/
Cellular line              &L0     Normal phone line
Data Set Ready
operations                 &S0     Override enabled
Break handling             &Y1     Clear buffer, send
                                   immediately

Stored telephone number    &Z0-9=s Blank
Pulse dial make/
break ratio                &P0     U.S./Canada
Guard tone                 &G0     U.S./Canada

Word length**              8
Parity**                   0    None
DTE rate** (Kbps)          19.2 --

**  Detected by the modem from the AT prefix of the &W com-
mand that writes your defaults to NVRAM.  Set your software
to the desired word length, parity, and serial port rate
defaults before sending the modem the AT . . . &W string.


Table B.4--&F3 HST Cellular Template

NVRAM Options            Setting   Description
------------------------------------------------------------
*Handshake option           B1     HST-mode/Bell answer
                                   tone
Normal/error control/sync  &M4     Normal/error control
Data compression           &K1     Enabled
Transmit data
  flow control             &H1     Hardware flow control

Rec'd data hardware
  flow control             &R2     Enabled
Rec'd data software
  flow control             &I0     Disabled
Serial port rate select    &B1     Serial port rate fixed
                                   higher than connect rate
Link rate select           &N0     Variable

Result code subset         X7      Extended.  Includes
                                   all codes except VOICE.

Protocol response codes    &A3     Full protocol codes
Tone/Pulse dialing         P       Pulse dial
Online local echo          F1      Disabled
Speaker control            M1      ON during dial through
                                   connect

Remote Digital
Loopback (RDL)             &T5     Deny RDL
*Normal/Leased/
  Cellular line            &L2     HST Cellular
*Carrier loss wait time     S10=30  Tenths of seconds

Data Set Ready override    &S0     Enabled
Break handling             &Y1     Clear buffer, send
                                   immediately

Stored telephone number    &Z0-9=s Blank
Pulse dial make/
  break ratio              &P0     U.S./Canada
Guard tone                 &G0     U.S./Canada

Word length**               8
Parity**                    0    None
DTE rate** (Kbps)           19.2 --

**  Detected by the modem from the AT prefix of the &W com-
mand that writes your defaults to NVRAM.  Set your software
to the desired word length, parity, and serial port rate
defaults before sending the modem the AT . . . &W string.



If DIP switch 10 is ON when the modem is powered on, or you
load factory template 0 (&F0), the following settings take
effect.  

Table B.5--&F0 No Flow Control Template

NVRAM Options            Setting   Description
------------------------------------------------------------
Handshake option           B0      ITU-T answer sequence
Normal/error control/sync  &M4     Normal/error control
Data compression           &K1     Enabled
*Transmit data
  flow control             &H0     Disabled

*Rec'd data hardware
  flow control             &R1     Disabled
Rec'd data software
  flow control             &I0     Disabled
*Serial port rate select    &B0     Detect from AT command:
                                   variable rate

Link rate select           &N0     Variable
*Result code subset         X1      Basic

*Error-control
  response codes           &A1     Enabled
Tone/Pulse dialing         P       Pulse dial
Online local echo          F1      Disabled
Speaker control            M1      ON during dial through
                                   connect

Remote Digital
  Loopback (RDL)           &T5     Deny RDL
Normal/Leased/
  Cellular line            &L0     Normal phone line
Data Set Ready
  operations               &S0     Override enabled
Break handling             &Y1     Clear buffer, send
                                   immediately

Stored telephone number    &Z0-9=s Blank
Pulse dial make/
  break ratio              &P0     U.S./Canada
Guard tone                 &G0     U.S./Canada

*Word length               7
*Parity                    1    Even
*DTE rate (bps)            9600 --

The word length, parity and DTE rate are detected by the
modem from the AT prefix of the &W command that writes your
defaults to NVRAM.  Set your software to the desired word
length, parity, and serial port rate defaults before sending
the modem the AT . . . &W string.
                                                  Factory
NVRAM S-Register Options                          Setting
------------------------------------------------------------
S0   Auto Answer                                  1
S2   Escape code character                        43
S3   Carriage Return character                    13
S4   Line Feed character                          10
S5   Backspace character                          8
S6   Dial wait-time, sec.                         2
S7   Carrier wait-time, sec.                      60
S8   Dial pause, sec.                             2
S9   Carrier Detect time, 1/10th sec.             6
S10  Carrier loss wait-time, 1/10th sec.          7
S11  Tone duration, spacing, msec.                70
S12  Escape code guard time, 1/50th sec.          50
S13  Bit-mapped functions                         0
S15  Bit-mapped functions                         0
S19  Inactivity/hang up timer                     0
S21  Break length, 1/100th msec.                  10
S22  XON character                                17
S23  XOFF character                               19
S24  Pulsed DSR duration, 2/100th sec.            150
S26  RTS/CTS delay time, 1/100th sec.             1
S27  Bit-mapped functions                         0
S28  V.32 handshake time, 1/10th sec.             8
S29  V.21 handshake time, 1/10th sec.             20
S32  Talk/Data Switch Options                     9
S33  Bit-mapped functions                         0
S34  Bit-mapped functions                         0
S38  Disconnect wait time, sec.                   0
S41  Allowable remote login attempts              0
S42  Remote Access ASCII character                126
S43  Remote guard time, 1/50th sec.               200
S44  Re-establish leased-line connect, sec.       15
S51  Bit-mapped functions                         0
S53  Bit-mapped functions                         0

*  Bit-mapped registers have up to eight functions.  See
descriptions later in this appendix or a briefer summary in
the Quick Reference Card.












S-REGISTER SUMMARY
------------------

Usage
-----
The default values are those users typically require.
Change the settings of an S-Register with the ATSr=n
command, where r is the register and n is a decimal value
from 0-255:
          ATS13=8 <Enter>

The modem does not perform a value-range check.  Some values
you select may not work with some equipment, and you'll have
to readjust the settings.

Some registers (S13, S14, S15, S16, S27, S34) are bit-mapped
(bits 0-7).  For example, turning on bit 0 of S13 causes the
modem to reset each time the computer or terminal drops its
Data Terminal Ready (DTR) signal.  Turning on bit 3 of S13
causes the modem, on receipt of DTR, to auto dial the number
stored at position 0 in NVRAM.

To turn on one or more bits in any bit-mapped register, use
the total of the values shown below.  For example, S13=9
turns on bits 0 (value of 1) and 3 (value of 8).

Alternatively, identify the bits to be turned on with the
following format:  Sr.b=1, where r is the register and .b is
the bit.  This format does not require knowledge of the
bit's value.  S13.0=1 .3=1 is the equivalent of S13=9,
above.  To turn off a bit function, set it to zero:
S13.0=0.

To display the contents of a register, use ATSr? as in this
example:
          ATS1?

To display the contents of a register, use ATSr? as in this
example:
          ATS19? <Enter>

Register       Default   Function                      
------------------------------------------------------------

S0             See DIP   Sets the number of rings on which
               switch 5  to answer when in Auto Answer mode.
                         S0=0 disables Auto Answer, the same
                         as DIP switch 5 ON (factory
                         setting).  S0=1 enables Auto Answer
                         and the modem answers on the first
                         ring.

                         NOTE:  If DIP switch 5 is OFF and
                         S0=0, Auto Answer remains disabled.
Register       Default   Function                      
------------------------------------------------------------

S1             0         Counts and stores the number of
                         rings from an incoming call.

S2             43        Stores the ASCII decimal code for
                         the escape code character.  Default
                         character is "+".  A value of 128-
                         255 disables the escape code.

S3             13        Stores the ASCII decimal code for
                         the Carriage Return character.
                         Valid range is 0-127.

S4             10        Stores the ASCII decimal code for
                         the Line Feed character.  Valid
                         range is 0-127.

S5             8         Stores the ASCII decimal code for
                         the Backspace character.  A value
                         of 128-255 disables the Backspace
                         key's delete function.

S6             2         Sets the number of seconds the
                         modem waits before dialing.  If set
                         to X2, X4, X6, or X7, the modem
                         dials as soon as it detects a dial
                         tone (fast dials).  If there is no
                         dial tone, the modem observes the
                         normal S6 timeout.

S7             60        Sets the number of seconds the
                         modem waits for a carrier.  May be
                         set for much longer duration if,
                         for example, the modem is
                         originating an international
                         connection.
















Register       Default   Function                      
------------------------------------------------------------

S8             2         Sets the duration, in seconds, for
                         the pause (,) option in the Dial
                         command and the pause between
                         command re-executions (> and A>
                         commands).

S9             6         Sets the required duration, in
                         tenths of a second, of the remote
                         modem's carrier signal before
                         recognition by the Courier.

S10            7         Sets the duration, in tenths of a
                         second,  that the modem waits after
                         loss of carrier before hanging up.
                         This guard time allows the modem to
                         distinguish between a line hit, or
                         other disturbance that momentarily
                         breaks the connection, from a true
                         disconnect (hanging up) by the
                         remote modem.

                         While we do not recommend
                         connecting the modem to a line with
                         call waiting, if you have call
                         waiting you may wish to adjust this
                         setting upward to prevent the modem
                         from misinterpreting the signal for
                         a second call as a disconnect by
                         the remote modem.  A better
                         alternative is to contact your
                         phone company to find out how to
                         temporarily disable call waiting.

S11            70        Sets the duration and spacing, in
                         milliseconds, of dialed tones.

S12            50        Sets the duration, in fiftieths of
                         a second, of the guard time for the
                         escape code (+++) sequence.












Register       Default   Function                      
------------------------------------------------------------
S13            0    Bit-mapped register.  Select the bit(s)
                    you want on and set S13 to the total of
                    the values in the Value column.  For
                    example, ATS13=20 enables bit 2
                    (value = 4) and bit 4 (value = 16).  Or
                    use ATSr.b=0 (OFF) or 1 (ON).  For
                    example, ATS13.0=1 .3=1 turns on bits 0
                    and 3.   To turn a bit off, set that bit
                    to zero, as in ATS13.3=0.

                Bit Value     Result
                0   1    Reset when DTR drops
                1   2    Reverse normal Auto Answer
                         operation:  on incoming RING, enter
                         Originate Mode and look for Answer
                         tone
                2   4    Disable 250 msec. pause before
                         result code display
                3   8    On DTR signal, Auto Dial the number
                         stored in NVRAM at position 0
                4   16   At power on/reset, Auto Dial number
                         stored in NVRAM at position 0
                5   32   Disable HST (used for testing V.32
                         terbo in Dual Standard modems)
                6   64   Disable MNP Level 3 (used for
                         testing Level 2)
                7   128  Custom applications

S14            0    Reserved.























Register       Default   Function                      
------------------------------------------------------------

S15            0         Bit-mapped register.  To set the
                         register, see the instructions for
                         S13.
                Bit Value     Result
                0   1    Disable the modem's extra high-
                         frequency equalization if it causes
                         problems on shorter-link calls--HST
                         mode only
                1   2    Disable online fallback
                2   4    Disable 450 bps back channel-- HST
                         mode only
                3   8    Reset non-ARQ mode Transmit buffer
                         from 1.5K bytes to 128*
                4   16   Disable MNP Level 4; retransmitting
                         the larger Level 4 data blocks may
                         be a problem if you expect a great
                         number of errors during a call
                5   32   Set backspace key to delete
                6   64   Some earlier 2400 bps MNP modems,
                         not made by U.S. Robotics or
                         Microcom, were not fully compatible
                         with the MNP protocol.  If you have
                         difficulty making a successful 2400
                         bps MNP connection with a remote
                         MNP modem, it may be because of
                         this incompatibility.  Set S15 to
                         64 and try again to make the
                         connection.
                7   128  Custom applications only

     * The default 1.5K byte non-ARQ buffer allows data
     transfer with X- and Ymodem-type file transfer
     protocols without using flow control.

     The 128-byte option allows remote users with slower
     modems to stop data you're transmitting from scrolling
     off their screens.  When remote users send your
     computer an XOFF (<Ctrl-S>) and you stop transmitting,
     the data in transit from your modem's buffer doesn't
     exceed the size of their screen.











Register       Default   Function                      
------------------------------------------------------------

S16            0         Bit-mapped test register.  To set
                         the register, see the instructions
                         for S13.  For information on
                         testing, see Appendix F.
                Bit Value     Result
                0   1    Analog Loopback
                1   2    Dial test
                2   4    Test pattern
                3   8    Remote Digital Loopback
                4   16   Reserved
                5   32   Reserved
                6   64   Reserved

S17            0         Reserved.

S18            0         Test timer for software-initiated
                         loopback testing (&Tn), disabled
                         when S18 is set to 0.  See Appendix
                         F.  Used to set the duration of
                         testing, in seconds, before the
                         modem automatically times out and
                         terminates the test.

S19            0         Sets the duration, in minutes, for
                         the Inactivity Timer.  The timer
                         activates when there is no data
                         activity on the phone line and at
                         the timeout the modem hangs up.
                         S19=0 disables the timer.

S20            0         Reserved.

S21            10        Sets, in 10-millisecond units, the
                         length of Breaks sent from the
                         modem to the computer.  Applies to
                         ARQ mode only.

S22            17        Stores the ASCII decimal code for
                         the XON character.

S23            19        Stores the ASCII decimal code for
                         the XOFF character.

S24            150       Sets the duration, in 20-
                         millisecond units, between pulsed
                         DSR signals when the modem is set
                         to &S2 or &S3.  The default is 3
                         seconds.



Register       Default   Function                      
------------------------------------------------------------

S25            0         Reserved.

S26            0         Reserved.
S27            0         Bit-mapped register.  To set the
                         register, see the instructions for
                         S13.
               Bit  Value     Result
               0    1    Enable ITU-T V.21 modulation at 300
                         bps for overseas calls.  In V.21
                         mode, the modem answers both Bell
                         103 and V.21 calls, but only
                         originates V.21 calls.
               1    2    Enable unencoded (non-trellis-
                         coded) modulation in V.32 mode;
                         this option is part of the ITU-T
                         V.32 recommendation, but is rarely
                         used.
               2    4    Disable V.32 modulation; used for
                         testing HST modulation in Dual
                         Standard modems.
               3    8    Disable 2100 Hz answer tone to
                         allow two V.42 modems to connect
                         more quickly.
               4    16   See below.
               5    32   See below.
               6    64   Reserved.
               7    128  Unusual software incompatibility.
                         Some software may not accept 7200,
                         12000, 14400, 16800, 19200 and
                         21600 bps result codes.  This
                         setting disables the codes and
                         displays the 9600 code instead.
                         The call's actual rate can be
                         viewed on the ATI6 screen.

                    Error control handshaking options:
                    select the total values of bits 4
                    and 5.

                    Bit 4     Bit 5     Result
                    0    0    Complete handshaking sequence:
                              V.42 Detection, LAPM error
                              control, MNP
                    16   0    Disable MNP
                    0    32   Disable V.42 Detection and
                              LAPM
                    16   32   Disable Detection phase, if
                              you know that the remote modem
                              does LAPM, but not the
                              Detection phase.

Register       Default   Function                      
------------------------------------------------------------

S28            8              Sets the duration, in tenths
                              of a second, of the extra
                              3000/600 Hz answer tones sent
                              during V.32 handshaking.
                              Default = 8 (.8     seconds).
                              This gives V.32 modems
                              additional time to connect in
                              V.32 mode before timing out.

                              If there is difficulty
                              answering older, manually
                              operated V.32 modems, for
                              example, modems that require a
                              button to be pushed in order
                              to dial, try lengthening the
                              duration of the extra tones.

                              Setting S28 to zero eliminates
                              the extra tones, resulting in
                              a faster connect time if, for
                              example, the modem is set to
                              use V.21 modulation (300 bps)
                              or V.23 modulation (1200 bps).

S29                 20        Not user definable.  Reserved
                              for U.S. Robotics' internal
                              use. 


S32                 9         Not user definable.  Reserved
                              for U.S. Robotics' internal
                              use.

S33                 0         Setting this register to 1
                              (S33=1) enables HST cellular
                              mode.















Register            Default   Function                      
------------------------------------------------------------
S34                 0         Bit-mapped register.  See
                              instructions for S13.
                         Bit  Value     Result
                         0    1    Disable V.32 bis.  Used
                                   for troubleshooting; U.S.
                                   Robotics' Technical
                                   Support may require that
                                   you disable V.32 terbo
                                   for testing purposes.    
                         1    2    Disable the modem's
                                   enhanced, U.S. Robotics
                                   proprietary V.32 bis
                                   modulation.  Used for
                                   troubleshooting
                         2    4    Disable the faster
                                   retrains that occur
                                   during proprietary V.32
                                   terbo modulation.  Used
                                   for troubleshooting
                         3    8    Enable V.23.  Required
                                   for some British
                                   connections
                         4    16   Reserved.
                         5    32   Reserved.
                         6    64   Disable the remote access
                                   busy message.
                         7    128  Disable V.32 terbo.

S38                      0         Sets the duration, in
                                   seconds, before a forced
                                   hang-up and clearing of
                                   the Transmit buffer, when
                                   DTR drops during an ARQ
                                   call.  This is provided
                                   to allow time for a
                                   remote modem to
                                   acknowledge receipt of
                                   all transmitted data.
                                   Default = 0:  the modem
                                   immediately hangs up when
                                   DTR drops.  If the modem
                                   receives the ATH command,
                                   it ignores S38 and
                                   immediately hangs up.








Register       Default   Function                      
------------------------------------------------------------

S41            0         Sets the number of allowable remote
                         access login attempts, thus
                         enabling or disabling remote
                         access.  The default setting of
                         zero allows no remote login
                         attempts, thus disabling remote
                         access.  A value of 1 or greater
                         enables remote access.  If the
                         number of unsuccessful login
                         attempts exceeds the limit set by
                         this register, the modem returns
                         online and any further login
                         attempts during the remainder of
                         that connection are refused.

S42            126       Stores the ASCII decimal code for
                         the remote access escape character.
                         The default character is a tilde
                         (~).

S43            200       Sets the duration, in fiftieths of
                         a second, of the guard time for the
                         remote access (~~~~) sequence.

S44            15        Sets the duration, in seconds, of
                         the delay between when the modem
                         senses loss of carrier and when it
                         attempts to re-establish a leased-
                         line connection.

S51            0         Bit-mapped register.  See
                         instructions for S13.
               Bit  Value     Function
               0    1    Disable MNP/V.42 for
                         V.22 (1200 bps)
               1    2    Disable MNP/V.42 for
                         V.22 bis (2400 bps)
               2    4    Disable MNP/V.42 for
                         V.32/V.32 bis/V.32 terbo
                         (9600/14,400/19,200/
                         21,600 bps)
               3-7  --    Reserved

S52            0         Reserved.







Register            Default        Function                 
---------------------------------------------------------

S53                 0              Bit-mapped register.
                                   Select the dial security
                                   features you want enabled
                                   by setting S53 to the
                                   total of the values in
                                   the Value column in the
                                   table below.  For
                                   example, S53=3 enables
                                   Dial Security with
                                   prompting.  S53=5 enables
                                   Dial Security and local-
                                   access password
                                   protection.  Or use
                                   ATSr.b=0 (OFF) or 1 (ON).
                                   For example, ATS53.0=1
                                   .2=1 turns on bits 0 and
                                   2.   To turn a bit off,
                                   set that bit to zero, as
                                   in ATS53.2=0.
                        Bit  Value     Result
                        0    1    Dial security enabled
                        1    2    Prompting enabled
                        2    4    Local-access password
                                  protection enabled
               


























+----------------------------------------------------------+
|                                                          |
|   APPENDIX C.  DIAL SECURITY AND                         |
|                REMOTE ACCESS OPERATIONS                  |
|                                                          |
+----------------------------------------------------------+

Dial Security is designed to protect networks and data
centers from unauthorized access.  A system administrator is
responsible for setting up to ten Dial Security accounts in
the modem's nonvolatile memory.

WARNING:  You must set up your local access security infor-
mation before enabling Dial Security, and allowing remote
calls, as outlined under Setting Up Security, after the
overview.  Be sure to remember your local access password;
if you enable security and forget your local access
password, you risk being locked out of your system.

OVERVIEW
------------------------------------------------------------

Autopass
--------
When the calling or remote user's modem is set for Dial
Security, it requests a V.42 error correcting connection,
and automatically sends an autopass password.

In order to use Autopass, the following requirements must be
met:
#    host and remote modems must be U.S. Robotics modems
     with Dial Security enabled.

#    a V.42 error correcting connection must be made.

Prompting
---------
Prompting allows a wider base of remote modems to connect
with the host U.S. Robotics Dial Security modem.  Instead of
sending an autopass password during the connection process,
the host modem prompts the remote user for a password.
Prompting is more flexible than autopass because it:

#    doesn't require a remote modem to have Dial Security.

#    doesn't require a V.42 connection, so remote modems
     without V.42 error control capabilities can connect.

     NOTE:  The host modem must be set for &M4 or &M5 in
     order to prompt remote users.  &M4 is recommended if
     calling modems do not support V.42 error control.



Optional Dialback
-----------------
Once a connection is made, the host disconnects and dials
back the remote modem at a predefined number or allows a
caller to specify a different dialback number, depending on
the security setup.

WHAT THE SYSTEM ADMINISTRATOR NEEDS TO DO
------------------------------------------------------------

Setting Up Security
-------------------
Before the system administrator activates Dial Security, the
following steps must be followed, in the listed order.
1.   Set up the system administrator's account, using one of
the accounts numbered 0-9.  Each account has five possible
fields, as shown in the following table.  In the example
below, the system administrator uses the name BILL as a
password.

Password  Account   Dialback  Allow New      Dialback
Enabled   Enabled   Enabled   Number              Number
------------------------------------------------------------
8 chars.  YES/NO    YES/NO    YES/NO         up to 37
max.                                         characters
ASCII                                        (0-9 #*,/:"!
32-127                                       PT@R)
case-
sensitive

BILL      Y    Y    N         1-419-555-5555

Use the %An= command and format below to set up accounts,
where n is the account number, 0-9.  The fields in the above
table are entered after the equal sign, each separated by a
comma, as in the following example for account 0 with the
password BILL.

WARNING:  Inserting spaces between commas or between fields
and commas will invalidate the command.
          AT%A0=BILL,Y,Y,N,1-419-555-5555 <Enter>

This example instructs the modem to store the configuration
for  account 0:  password (BILL), account enabled (Y),
dialback enabled (Y), allow a new number (N), and the
dialback phone number.

NOTE:  The %An= command is automatically written to NVRAM
and does not require an &W.

Each function can be configured or modified independently.
If a field is to remain blank, just insert a comma, as shown
in the following command which allows the remote user to
supply a new number different from the dialback number
stored in the account record.
          AT%A0=,,,Y, <Enter>

Some accounts may have fewer security options.  The
following example sets the password (Judy) and enables
account 1 without any dialback options.
          AT%A1=Judy,Y,,, <Enter>

2.   Set up your local access password.  This password,
     which protects the integrity of the accounts by denying
     access by other users, must be one of the enabled
     account passwords, and must be chosen before Dial
     Security is enabled.

     The local access password is set with the %L= command.
     In the following example, the local access password is
     the same as the password in account 0, BILL.
          AT%L=PW0 <Enter>

3.   Enable local access password protection by turning on
     bit 2 of Register S53.
          ATS53.2=1 <Enter>

     NOTE:  Once enabled, remote users cannot change the
     local access password.  If local access password
     protection is not enabled, remote users can get into
     the host modem and change account information,
     including erasing all accounts.

     In addition, enabling local access password protection
     disables the &Zn=s command which stores up to ten phone
     numbers, and occupies the same space in NVRAM as the
     dialback numbers for Dial Security accounts.

     If the local access password is not protected, the
     &Zn=s command overwrites the corresponding Dial
     Security dialback number.  For example, the following
     command overwrites the dialback number for account 5.
          AT &Z5 = 555-8976 <Enter>

     However, if the local access password is protected, and
     a user tries to use the &Zn=s command, an ACCESS DENIED
     message is displayed.

4.   Set up the remote users' accounts with the %An=
     command, using the guidelines found in step 1.

5.   Enable Dial Security, choosing either autopass, or
     prompting as an option.  The system administrator must
     know what types of modems are being used by remote
     users and set the Dial Security parameters accordingly.
     Autopass is limited to U.S. Robotics modems with Dial
     Security, and prompting is not.

Register S53 is used to enable Dial Security, and is a bit-
mapped register.  Select the Dial Security options you want
and set S53 according to the table below.

          Bit  Result
          ------------
          0    Dial security enabled.
          1    Prompting enabled when bit 0 is on.
          2    Local-access password protection enabled
               when bit 0 is on.
          
          Table C.1--Dial Security Functions for Host

The &W command must be used to save Register S53 settings to
NVRAM.  Otherwise, when the computer is powered off and on
again, or the modem is reset using ATZ, it will default to
S53=0, Dial Security disabled.

To enable autopass with local access password protection,
but without prompting, type the following command.
          AT S53.0=1 .2=1 &W <Enter>

The following command enables Dial Security with prompting,
and local access password protection.
          AT S53.0=1 .1=1 .2=1 &W <Enter>

6.   Check to see that DIP switch 10 is OFF (factory
     setting) so that the modem loads the settings stored in
     NVRAM, as well as Dial Security information.

     WARNING:  If someone sets DIP switch 10 ON, the factory
     read-only (ROM) defaults are loaded, and Dial Security
     is disabled.  If this should happen, reset DIP switch
     10 to OFF, power off the computer and power it back on,
     or reset the modem by typing ATZ <Enter> so that the
     proper setting takes effect.

LOGIN OPERATIONS
------------------------------------------------------------

Autopass
--------
Autopass is only possible between two U.S. Robotics modems
with Dial Security.

When autopass is enabled, the remote modem must send a valid
autopass password in order to connect.

If a remote user has set up the modem with an invalid
password, or has failed to enable Dial Security, the host
modem returns an Invalid Password message and hangs up.



Prompting
---------
When prompting is enabled, a remote caller must match one of
the account passwords to connect.

If the remote modem doesn't have error control capabilities,
the host modem will still allow a connection, provided the
host is set to &M4 so it can also answer non-error
correcting calls.

If the modems are compatible, the host modem prompts the
caller for a password, and waits 60 seconds before
disconnecting.  The host modem checks the received password
against each of its active Dial Security accounts.  If the
password is invalid, the host modem prompts twice more
before disconnecting.

Optional Dialback
-----------------
When the host modem receives a valid password, and an
account's dialback field is enabled, the host disconnects.
The remote user receives a NO CARRIER message.  Then the
host modem dials back the remote modem, typically at the
number stored in the phone number field.  The dialback
process takes approximately one minute due to telephone
company requirements.

However, if the account allows a new number, the host
prompts the remote user for the new number before hanging
up, and then dials back.

ACCOUNT MAINTENANCE
------------------------------------------------------------

Once the local access password is set and protected, the
system administrator is the only one who can access account
information.  To modify or change account information, use
the %S= and %E= commands described next.

ACCOUNT ACCESS (%S)
------------------------------------------------------------

The system administrator can access accounts one of two ways
once Dial Security is enabled:

#    disable Dial Security and edit the accounts using the
     %An= command.

#    enter your local access password using the %S= command,
     which allows access to the accounts without disabling
     security.

     AT%S=(your local access password) <Enter>

     NOTE:  The modem echoes the local access password,
     which is case sensitive.  If the password is Bob and is
     entered as BOB, for example, an OK is displayed.
     However, if you try to type another command, for
     example,  ATI10 <Enter> to view accounts, an Access
     Denied message is displayed.  Be sure to enter the
     password in the exact way as it was set up.

     Once access has been granted you can view and/or edit
     account information using the following commands.

ACCOUNT STATUS
------------------------------------------------------------

To view account information, type the following command.
          ATI10 <Enter>

This command is only valid for remote users if local access
security is disabled.

ERASING ACCOUNT INFORMATION (%E)
------------------------------------------------------------

Use the %E= command to make system edits.

%E=1 Erases local access password.
%E=2 Erases autopass password.
%E=3 Erases passwords in accounts 0-9.
%E=4 Erases phone numbers in accounts 0-9.
%E=5 Disables Account, Dialback and New Number
     fields in accounts 0-9 disabled.

To edit or overwrite an individual account, or an individual
account field, use the %An= command described in Setting Up
Accounts, earlier in this appendix.

REMOTE CONFIGURATION
------------------------------------------------------------

To remotely configure Dial Security accounts, see
Configuring Dial Security Remotely at the end of this
appendix.

DIALING IN
------------------------------------------------------------

Remote users must perform the following operations in order
to call into the host's Dial Security system.

1.   For prompting, get a password from the system
     administrator.  For autopass, get a password or account
     number (0-9) from the system administrator.  Passwords
     are case-sensitive, so be sure to copy it down
     correctly.  For prompting, skip to step 3 if the
     administrator enables dialback for your account.

2.   For autopass only.  Set up the remote modem to send the
     autopass password during the connection sequence, using
     the %V= command as in the following example.
          AT %V=Ryan <Enter>

     Alternatively, just use your the account number as the
     autopass password, as in the following example.
          AT %V=PW9 <Enter>

     NOTE:  It doesn't matter if the autopass password is
     the same as the system administrator's local access
     password.

     You can check to see that you've correctly set up your
     autopass password by typing the following command.
     Your autopass password appears in the righthand column
     below FORCED AUTOPASS.
          AT I10 <Enter>

     Once the autopass password is set, Dial Security must  
     be enabled with the following command.
          ATS53.0=1 &W <Enter>

3.   Set the modem to automatically answer incoming calls--  
     only if dialback is enabled.

     If the host modem qualifies an autopass password, and
     dialback is enabled, the host disconnects the incoming
     call and dials back the remote caller.  This process
     usually takes about one minute due to telephone company
     requirements.

     The Courier is shipped with DIP switch 5 ON, Auto
     Answer suppressed.  To set the modem to automatically
     answer incoming calls, set DIP switch 5 OFF and reset
     the modem (ATZ <Enter>).

     Or set the modem to answer on the first ring by typing
     the following command, and save it to NVRAM with the &W
     command.
          AT S0=1 &W <Enter>











------------------------------------------------------------
REMOTE ACCESS OPERATIONS
------------------------------------------------------------

You can set a Courier modem so that it can be remotely
configured by someone at another modem.  This is especially
helpful when you have problems making a connection with
another modem.  For example, if you have trouble connecting
with a bulletin board, you can allow the bulletin board
operator to dial in to your modem and view its configuration
settings.  If necessary, the bulletin board operator can
send the Courier a configuration string to correct your
settings.  Another use might be for Dial Security
administration when the system administrator is unable to be
at the host modem site.  It might be urgent, for example, to
disable an account.

AT THE COURIER SITE
------------------------------------------------------------

Setting the Courier for Remote Access
-------------------------------------
There are two tasks required to use remote access:

#    set up password security

#    enable remote access

Password Security
-----------------
You can designate two passwords for remote access security,
each allowing a different level of access to the remote
user.  You can assign one password that allows viewing
privileges only, whereby the Courier's configuration can be
remotely viewed but not changed.  You can assign another
password that allows both remote viewing and configuration
privileges.

Passwords can be up to eight alphanumeric characters long,
and are not case-sensitive.  To assign a password that
allows viewing privileges only, use the following command
format.
          AT%P0=[password] <Enter>

To assign a password that allows viewing and configuration
privileges, use this command format.
          AT%P1=[password] <Enter>

Enabling Remote Access
----------------------
Register S41 designates the number of allowable login
attempts by the remote user, thus enabling or disabling
remote access.  If the number of allowable login attempts is
set to 0, remote access is disabled.
If the number of unsuccessful login attempts exceeds the
limit set in S41, the modem returns online and any further
login attempts during the remainder of that connection are
refused.

Disabling Password Security
---------------------------
If you want to disable an assigned password (and thereby
disable remote access security), use the following command
format.
          AT%P0= <Enter>
               or
          AT%P1= <Enter>

If, for example, you disable the %P0 password, a remote user
does not need to enter a password for view-only access.

At the Remote Modem Site
------------------------
Remote configuration can be performed at any time during an
asynchronous connection.  The user performing remote
configuration can use any modem; it does not have to be a
U.S. Robotics model.

1.   Make sure the Courier has been set for remote
     configuration, as described earlier, and establish a
     connection.  It does not matter which modem originates
     the call.

2.   After a connection has been established, send the
     following escape sequence.

     Pause four seconds,
     type four tildes: ~~~~
     and
     pause another four seconds.

     NOTE:  You can change the escape sequence character
     with Register S42.  The pause duration (guard time) can
     be modified with Register S43.  (These values are set
     at the Courier modem.)

3.   When the Courier begins its login sequence, the caller
     will see a display similar to the following.

     U.S Robotics Courier HST Dual Standard terbo Fax Remote
     Session
     Serial Number 000000A000000001

4 .  At this point, if password security is active, the
     caller is prompted for the password.

     Password (Ctrl-C to cancel)?.....

     As described earlier in Password Security, entering the
     password assigned with %P0 allows viewing privileges
     only.  Entering the password assigned with %P1 allows
     viewing and configuration privileges.  Note that there
     is a 3-minute time limit for entering the password.

     As mentioned earlier, if the number of unsuccessful
     login attempts exceeds the set limit, the modem returns
     online and refuses any further login attempts during
     the remainder of that connection.

     When a password is accepted, the Courier indicates that
     it has entered Remote Access mode and the remote prompt
     appears on the caller's screen.

          Access Granted
          Remote->

5.   If password security is not active (no passwords have
     been set or both passwords are disabled), the Courier
     automatically enters Remote Access mode and the remote
     prompt appears on the caller's screen.

     Remote->

6.   Once the remote access session has been established,
     keep in mind that there is a 3 minute inactivity timer.
     If the modem detects no activity for 3 minutes, it
     aborts the remote access session and resumes a normal
     online connection.

Aborting the Request for Remote Access
--------------------------------------
You can abort the remote access login procedure and return
online by pressing the key combination <Ctrl>-C.

Remote Viewing and Configuration
--------------------------------
Once you've gained remote access, you can communicate with
the Courier as if you were typing commands at its attached
computer.  Depending on your access privileges, you can use
the regular Courier AT commands.

If you have view privileges only (with Password 0), you can
use any of the view commands described in Chapter 5.

If you have view and configure privileges (set with %P1),
you can use any of the modem commands, except those commands
that cannot be used while online, such as the Dial command.
You can also use the remote access commands explained later.

When you make remote configuration changes, the remote


prompt is altered to indicate that changes have been made.
The prompt will change from:

     Remote->
               to
     Remote+>

If you restore the original configuration (with %C1,
explained next), the original prompt is also restored (back
to Remote->), indicating that the original configuration is
intact.

By default, configuration changes do not take effect until
the connection is terminated (see %Cn).  However, the new
configuration is immediately reflected in the information
screens (ATIn).

REMOTE CONFIGURATION COMMANDS
------------------------------------------------------------

There are some additional commands that are only executable
during a remote access session.  These commands are as
follows.

%Bn  Configure the Courier's serial port rate.

     %B0  110 bps.       %B6  9600 bps.
     %B1  300 bps.       %B7  19,200 bps.
     %B2  600 bps.       %B8  38,400 bps.
     %B3  1200 bps.      %B9  57,600 bps.
     %B4  2400 bps.      %B10 115,200 bps.
     %B5  4800 bps.

%Cn  Configuration control.

     %C0  Defer configuration.   This is the default.
          Configuration changes are deferred until the call
          is ended, and take effect for ensuing connections.
          You do not need to enter this command; it is the
          default unless you enter one of the following %C
          values.

     %C1  Restore configuration.  Use this command to cancel
          any configuration changes made during remote
          access, and restore the original configuration.
          However, commands that have been written to NVRAM
          (with &W) will not be restored to their previous
          settings.  Additionally, if you have forced
          immediate configuration changes (with %C2), those
          changes cannot be reversed with %C1.

     %C2  Execute configuration.  Use this command to force
          configuration changes to take effect immediately,
          during the current connection.  We recommend
          against forcing immediate configuration changes
          unless absolutely necessary, as this can result in
          an unreliable connection or even a loss of
          connection.

%Fn  Configure data format.

     %F0  No parity, 8 data bits.

     %F1  Mark parity, 7 data bits.

     %F2  Odd parity, 7 data bits.

     %F3  Even parity, 7 data bits.

Password Commands
-----------------

%Pn=      Disables password security (n=0 or 1) when no
          character follows the equal sign.

%Pn=s     Specify the following password string (s) for
          viewing privileges only (n = 0) or view and
          configuration privileges (n= 1).

%Pn?      Display password n.

Command Format
--------------
When typing commands during the remote access session, no
delay between command strings is necessary.  For example,
you can type the following commands without pausing after
each one.

#    a password:  ABCDEF <Enter>

#    a configuration string: AT&H1&R2&W <Enter>

#    and a request for an information screen: ATI5 <Enter>

The maximum number of characters between carriage returns is
40.

Ending a Remote Access Session
------------------------------
One of three commands ends a remote access session.

#    ATZ resets the modem and terminates the connection.

#    ATH terminates the connection.

#    ATO ends the remote access session, but the modems
     remain online.

CONFIGURING DIAL SECURITY REMOTELY
------------------------------------------------------------

The system administrator can configure account information
from a remote site, using the following procedures.

NOTE:  Before remote configuration is possible, the local
modem's remote access must be enabled, and a remote access
password that allows viewing and configuration privileges
must be assigned.  For convenience, you may want to use your
local access password as your remote access password.

Dialing In From the Remote Site
-------------------------------

1.   From the remote site, connect to the host modem using
     Dial Security.  Once a connection is made, follow the
     instructions for beginning a remote access session as
     described later in this appendix.

2.   When remote access has been granted, use the %S=
     command to access the Dial Security accounts.

3.   If you wish, you can view account information by typing
     the following Inquiry (I) command.
          AT I10 <Enter>

4.   Make any configuration changes and save them
     immediately by typing the following command.
          AT %C2 <Enter>

5.   To end the remote session and reactivate local access
     security on the host modem, reset the modem by typing:
          ATZ <Enter>

     WARNING:  If you do not use the ATZ command to end a
     remote access session, Dial Security will remain
     disabled and anyone dialing in to the local modem will
     have access to all Dial Security accounts.















+----------------------------------------------------------+
|                                                          |
|   APPENDIX D.  TROUBLESHOOTING                           |
|                                                          |
+----------------------------------------------------------+

You may occasionally encounter one of the problems listed
here.  They are divided into two categories:  before and
during the exchange of user information over the data link.

BEFORE ESTABLISHMENT OF THE DATA LINK . . .          
------------------------------------------------------------

Your modem doesn't answer the phone or go off hook to dial a
number
------------------------------------------------------------
Review the STOP guide that came with the modem or your
communications software manual to see what Data Terminal
Ready (DTR) operations your software requires.  Then check
to see if DIP switch 1 is set correctly.

Doesn't respond OK when you type AT <Enter>

1.   Make sure you're typing in either upper case or lower
     case letters, not a combination, and that you press the
     Enter key.

2.   Make sure your computer is in Terminal mode.  This is a
     communications software function.  See Testing the
     Modem in Chapter 2.

3.   Check to see that your software is set to the correct
     bit rate and word length (7 bits with or without a
     parity bit, or 8 bits and no parity).  Also make sure
     your software is set to the correct communications
     (serial) port, as determined in the setup instructions
     in Chapter 2, under Selecting a Serial Port.

4.   Check that DIP switch 8 is ON, for command set recog-
     nition.  If the switch is OFF, power off the computer,
     set the switch ON, and power on the computer again.
     Try typing AT <Enter> again.

5.   Check that DIP switch 3 is ON, for result code display,
     and that DIP switch 2 is OFF, for verbal result codes.
     If not, change the switch(es) and type ATZ <Enter>.  Or
     type whichever of these commands is needed:
     ATQ0 <Enter>   (to enable the message)
     ATV1 <Enter>   (to display a verbal message)

6.   Review the STOP guide that came with the modem or your
     communications software manual to see what Carrier
     Detect (CD) operations your software requires.  Then
     check to see if DIP switch 6 is set correctly.
Your modem displays double characters
-------------------------------------
Both your modem's and software's local echo are on.  You can
turn your software's local echo off.  Or turn the modem's
echo off by either resetting DIP switch 4 and sending the
modem the ATZ command, or by sending the modem the ATE0
command.

Your computer reacts as though a data link has been
established, but no call has been received
----------------------------------------------------
DIP switch 6 is set ON at the factory for Carrier Detect
(CD) override, but your system may require that the override
be turned OFF.

Review the STOP guide that came with the modem or your
communications software manual to see what CD operations are
required.  Then check to see if DIP switch 6 is set
correctly.

When the modem is in Answer mode, acts if a Carriage Return
has been entered, but nothing has been typed at the keyboard

Your software may be misreading signals from the modem as it
automatically sends a Carriage Return and a Line Feed before
and after the RING and CONNECT messages.  Sending the Quiet
Mode command, ATQ1 <Enter>, should solve the problem.

BOTH MODEMS . . .
------------------------------------------------------------

Exchange carrier signals, but fail to establish a
communications link
--------------------------------------------------
1.   If you have a fax modem, make sure it is in the correct
     mode, fax or data, depending on whether the connection
     is to be made with a facsimile device or a data modem.
     See Fax Operations in Chapter 4 for information on
     switching between fax and data modes.

2.   Check to make sure the proper bit rate, word length,
     parity and number of Stop bits have been selected.

3.   Check to see that your modem is at the correct Bn
     setting to connect with either an HST modem (B1
     setting) or V.32 modem (B0 setting).  Type ATI4 for a
     display of the Courier's current settings and, if
     necessary, send the modem the correct setting.

4.   Depending on your modem type, make sure the modem at
     the other end of the line is V.32 bis-compatible or
     USR-HST-compatible at 14.4 Kbps, V.32-compatible at
     9600 bps, V.22 bis-compatible at 2400 bps, Bell 212A-
     compatible at 1200 bps, or Bell 103-compatible at 300
     bps.  These are the common signaling standards for full
     duplex dial-up network transmission in the U.S.

5.   If your modem is attempting to answer a V.32 call, you
     may need to lengthen the extra V.32 answer tones.  See
     S28 in Appendix B.

6.   Make sure your modem's link rate setting, &Nn is
     correct for the call.  If the link rate is locked at a
     speed (&N1-&N9) different from the calling modem's, the
     Courier hangs up.  The factory setting of &N0, variable
     link operations, allows the two modems to negotiate the
     highest possible link rate.

7.   If none of the above corrects the problem, it's likely
     that the quality of the phone connection is poor and
     that the other modem is missing the signals your modem
     is transmitting.  The variable quality of phone line
     connections may be due to any number of conditions in
     the phone service's equipment or the current
     environment.  Try several calls, and if you still can't
     get through, try calling another modem.  If the second
     modem accepts your call, the problem may lie with the
     modem you first tried to call.

During Data Transfer Your Screen Displays . . .
------------------------------------------------------------

Only brackets
-------------
Check to make sure that both modems are set to the same bit
rate, word length, parity and number of Stop bits.  If the
settings are correct, the problem may be with the phone
line.  Try the following measures:

1.   Try placing the call again.  The phone company routes
     even local calls differently each time you call.

2.   Try calling a different modem to see if the problem
     persists.  The problem may be with the modem you first
     tried to call.

Random or garbage characters
----------------------------
Check to make sure that both modems are set to the same bit
rate, word length, parity, and number of Stop bits.

If the modem is set to a fixed serial port rate (&B1) and
your software is fixed at 19.2, 38.4, or 57.6 Kbps, the
reason may be one of the following:

1.   Your computer may not support the high rate.  If this
     is the case, fix your software rate at 9600 bps and

     disable high-speed V.32 bis modulation:  ATS34=3 or
     ATS34 .0=1 .1=1.

2.   If you use memory-resident programs (TSRs), they may be
     interfering.  Try disabling them before you run your
     communications software.  The same is true of disk-
     caching programs.

3.   Check to see that your software and the modem are set  
     for the same kind of flow control, either hardware or
     software.  Some communications programs also require
     that you disable the kind you are not using.

Double characters
-----------------
Your modem's online local echo is on and the remote modem is
also echoing.  The only way to correct this is to bring the
modem back to Command mode (wait one second without
transmitting data, type +++, wait another second).  Then
type the command to turn off your online echo (ATF1
<Enter>).

If DIP switch 9 is OFF (factory setting), the modem hangs up
when it returns to Command mode, and you'll have to call
again.  If DIP switch 9 is ON, the modem maintains its
connection.  You can return it back online by typing ATO
<Enter>.

IF YOU STILL HAVE PROBLEMS    
------------------------------------------------------------

The problems described above are by far the most common ones
that users encounter.  If the suggestions we've given don't
clear up your difficulties, try the following:

1.   Review the manual carefully to see if you've missed
     something.

2.   Call or visit your dealer.  Chances are your dealer
     will be able to give you the assistance you need.  This
     is much more efficient and time-saving than returning
     the modem to U.S. Robotics.

3.   If your dealer can't clear up your difficulties, call
     the U.S. Robotics Technical Support Department at 800-
     982-5151, or send a fax to 708-982-0823.  Our Service
     Representatives will be happy to give you assistance
     over the phone Monday through Friday from 8:00 a.m. to
     6:00 p.m. (Central Time Zone).

4.   If necessary, the Service Representative you talk to
     may give you a Return Materials Authorization (RMA)
     number.  Modems without an RMA number will not be
     accepted.
5.   If you do return the modem to us, please use the
     following procedures.

     a.   Ship the unit, postage paid, in its original
          container.

          If the original container is not available, pack
          the modem carefully in a strong box of corrugated
          cardboard with plenty of packing material.

     b.   Be sure to include your RMA number inside the
          package, along with your name and address.  Put
          your return address and your RMA number on the
          shipping label as well.

     c.   Ship the well-packed modem to the following
          address.

          Technical Support Department
          U.S. Robotics, Inc.
          8100 North McCormick Boulevard
          Skokie, Illinois 60076-2999

     d.   Please note that U.S. Robotics will not accept
          packages sent COD, so be sure to send the modem
          postage paid.

     e.   U.S. Robotics will repair your modem and return it
          to you via United Parcel Service.

























+----------------------------------------------------------+
|                                                          |
|   APPENDIX E.  ADDITIONAL OPERATIONS                     |
|                                                          |
+----------------------------------------------------------+

CONTENTS
------------------------------------------------------------

Dedicated and Leased Line Operations
HST Cellular Operations
Voice/Data Communications
Hewlett Packard 3000 Installations









































------------------------------------------------------------
DEDICATED AND LEASED LINE OPERATIONS
------------------------------------------------------------

The following operations apply in installations where the
modem's phone line is not part of a public-access switched
telephone network.  Instead, the modem is connected to a
special user-installed telephone line or a line that is
leased from the telephone company.  These lines are often
referred to as dedicated (to a pair of modems) or private
lines.

In both types of installation there is a continuous point-
to-point connection between two modems.  No dialing of phone
numbers is required.  The modems may be in either Smart or
Dumb mode (determined by the position of DIP switch 8).

The User-Installed or Leased Telephone Line
------------------------------------------------------------
User-installed lines are most commonly 2-wire lines, similar
to the 2-wire lines that connect residential phones to the
public switched network.

If you are leasing a line from the telephone company,
request a 2-wire line, the type of line the modem is
designed to work with.  If the telephone company only makes
a 4-wire line available, you'll need a 4-wire to 2-wire
converter at each end of the connection.  If the phone
company does not install the converters, you will have to
supply them.

For optimal operations, we recommend that the physical
length of these lines not exceed 5 miles.

Setting the Modem
-----------------
If the Courier is set to &L1, as described in what follows,
and the remote AT-compatible modem has a comparable setting,
they automatically connect when they are powered on.  They
also reconnect, without any operator intervention, if a
disturbance on the line is severe enough to break the
connection.

Set the modem as follows:

1.   Set your computer or communications software to the
     rate at which you want the modems to communicate.  For
     example, use a computer/software setting of 19.2K bps
     and, if both modems have the capability, they will
     connect at 14.4K bps.  The following instructions
     assume that you are familiar with the guidelines on
     using the &Bn and &Hn commands (Chapter 3) and the &W
     command (Chapter 3).

2.   Send the modem the following command:
          AT &B1 &S2 &H1 &L1 &W <Enter>

     &B1 fixes the modem's computer interface rate at 19.2K
     bps.  &S2 causes the modem to send a Clear to Send
     (CTS) signal only after it sends the Carrier Detect
     (CD) signal, that is, only after it connects with the
     remote modem.  (See the note that follows.)  &H1
     enables hardware (CTS) flow control.
     
     &L1 forces the modems off hook at power on and enables
     them to re-establish the connection should it be
     broken.  &W writes the settings to nonvolatile memory
     (NVRAM) as power-on defaults.

     NOTE:  We recommend using the &S2 setting, to delay CTS
     until after the connection is made, as a precaution.
     If the modems are in the process of connecting or
     reconnecting, the Courier interprets any keyboard data
     entry, including an accidental key stroke, as a key-
     press abort, and hangs up.  Delaying CTS until after
     carrier detection prevents this from happening, for
     example, if you are typing data to the remote modem
     when the modems momentarily disconnect and begin to
     reconnect.  However, you have to set the modem for
     hardware flow control, &H1.

     If your software or machine does not support Clear to
     Send (CTS), don't include &S2 and &H1 in the command
     string as suggested above.  Follow the Transmit Data
     flow control (&H) guidelines in Chapter 3.  But keep in
     mind that if the modems fail to connect or reconnect,
     the reason could be a key-press abort.

3.   Set the modem to load NVRAM settings at power-on, DIP
     switch 10 OFF.  It does not matter if the modem is in
     Dumb or Smart mode (DIP switch 8).

4.   Decide which modem is to be the calling modem and which
     the answering modem.  Set the answering modem to Auto
     Answer, DIP switch 5 OFF, and the calling modem to Auto
     Answer suppressed, DIP switch 5 ON.

5.   Power off and power on the modems.  This initiates the
     new DIP switch settings and loads the power-on
     defaults, including &L1.  The modems go off hook and
     establish the connection.

     NOTE:  If the modems cannot restore the connection and
     you could not set the modem to &S2, the reason could be
     a key-press abort.  If the problem persists, however,
     you may need to call your telephone company to have
     them check your line.

------------------------------------------------------------
HST CELLULAR OPERATIONS
------------------------------------------------------------

This function applies to Dual Standard HSTs only.  HST
cellular modems can be used to answer or originate calls,
but are proprietary.  They can only connect with other U.S.
Robotics Dual Standard modems with HST cellular
capabilities.

To enable cellular mode, load the factory setting template 3
by typing the following command.
          AT &F3 <Enter>

To save this as your power-on/default setting, type this:
          AT &F3 &W <Enter>

The &F3 command sets the serial port rate to 19,200 bps, and
formats the data for 8 bits, no parity and one stop bit.
The ini-tialization string sent to the modem is shown below.
          AT B1 X7 S10 = 30 &B1 &L2 &H1 &I0 &R2

#    B1--enables HST modulation.
#    X7--displays extended result codes including NO DIAL
     TONE, RINGING, NO ANSWER, and BUSY messages.
#    &B1--sets the serial port rate so that it remains 
higher
     than the connection rate.
#    S10=30--sets the modem to wait 3 seconds after loss of
     carrier before hanging up.
#    &L2--enables cellular mode.
#    &H1--enables hardware flow control.
#    &I0--disables software flow control.
#    &R2--sets the modem so it sends received data to the
     computer when the Ready To Send (RTS) signal is high,
     only if the computer supports RTS.

The modem uses the U.S. Robotics proprietary HST cellular
protocol to make connections.  The call starts at 1200 bps,
a V.42 error control connection is negotiated, then the
modem switches to 4800 bps and begins measuring the line
conditions.  Depending on line conditions, the modem
decreases or increases its connection rate, to a minimum
speed of 300 bps and a maximum of 12K bps.  If a connection
terminates before data transfer is completed, the system
tries to re-establish the link and complete the transfer.

If a large number of blocks are being resent (some software
displays the blocks retransmitted in the file transfer
window), you may want to reduce the packet size by doing the
following:

1.   Be sure DIP switch 9 is ON so that the modem remains
     online if it receives +++.

2.   If DIP switch 9 is OFF, switch it to ON and reset the
     modem by issuing the ATZ command.

3.   Send the modem the escape sequence by typing +++ so
     that the transmission is interrupted, and wait 1
     second.

4.   Type AT S33=1 <Enter> to reduce the packet size.

5.   Then type ATO <Enter> so that the modem returns online
     and continues to transmit.

NOTE:  HST cellular connections can only be made with other
U.S. Robotics modems in HST cellular mode.  The modem cannot
be used to place a voice or data call to another phone or
modem when it is in this mode.






































------------------------------------------------------------
VOICE/DATA COMMUNICATIONS
------------------------------------------------------------

When you install the Courier, you have the option of plug-
ging your phone into the second modular jack of the modem so
it's available for voice calls.  You can also use the phone
to set up communications with another user whose modem uses
the AT command set, such as a U.S. Robotics-compatible
modem.

Preparation
-----------
First call the other user to establish the bit rate, parity,
word length and number of Stop bits the other person's modem
accepts.  Then both of you can turn the call over to your
modems.

Commands
--------
1.   Without hanging up the phone, have your modem go off
     hook in Originate mode.  Type the following command:
          ATD <Enter>

     NOTE:  Be sure the modem is not set to X2, X4, X6, or
     X7, or it will return the NO DIAL TONE result code and
     hang up.

2.   The other party should then have the remote modem go
     off hook in Answer mode.  The following command is used
     to do this:
          ATA <Enter>

3.   Now both of you can hang up your respective phones
     while the modems establish the data link.  They will
     maintain the link until one of you gives your modem a
     command to disconnect.

     Either party's device can be the originate or answer
     modem:  it doesn't matter who made the phone call.  But
     one modem must first enter Originate mode and the other
     then enter Answer mode.  You and the other party,
     therefore, must agree on which command, ATD or ATA, you
     will each use.










------------------------------------------------------------
HEWLETT PACKARD INSTALLATIONS
------------------------------------------------------------

During error control connections, the Courier recognizes the
ASCII ENQ/ACK characters exchanged between many Hewlett
Packard host computers and their terminals.  The HP host
sends the terminal an ENQ character at predefined intervals,
and sends no more data until the terminal responds with an
ACK character.

Courier modems manage this ENQ/ACK protocol so that
communication is speeded up, thereby enabling HP terminals
to achieve high speeds on dial-up lines.  Special flow
control settings, using the &I command, are required for HP
users.  These settings apply to ARQ connections only and to
Courier modems set to either B0 or B1.  Disregard other
Courier flow control commands.

Set the Courier to Host mode if it is attached to the host
computer, or to Terminal mode if it is attached to a
terminal, as follows:

     Host mode      AT&I3 <Enter>

     Terminal mode  AT&I4 <Enter>




























+----------------------------------------------------------+
|                                                          |
|   APPENDIX F.  MODEM TESTING                             |
|                                                          |
+----------------------------------------------------------+

Testing is available with the &T command or Register S16.
All loopback testing conforms to ITU-T Recommendation V.54.
Earlier U.S. Robotics high speed modems, however, did not
perform the &T test repertoire.

Only one test can be performed at a given time.  If you send
a test command while the modem is in test mode, you'll
receive an ERROR message.

TESTING WITH &Tn
------------------------------------------------------------

The tests supported through the &T command include analog
loopback, digital loopback and remote digital loopback.
Users can key in their own data during testing, or use the
modem's internal test pattern and error detector.

In all cases, disable error control before testing.  If the
modem is detecting errors and retransmitting the affected
data, your results will be invalid.

Ending a Test--&T0, S18
----------------------
Issuing the &T0 command terminates a test.  Alternatively,
set Register S18 to a specified number of seconds, for
example, S18=10.  When the 10 seconds are up, the modem
automatically ends the test and returns to Command mode.  If
the test was Analog Loopback, the &T0 command hangs the
modem up.  If the test was Digital or Remote Digital
Loopback, issue an ATH command to hang up the modem, or an
ATZ command to hang up the modem and reset it to its
defaults.

NOTE:  If you use the S18 test timer, but in the process of
testing you issue an ATZ command, S18 resets to zero and the
timer is disabled.  You cannot store a value for S18 in
nonvolatile memory:  its power-on and reset default is
always zero.

ANALOG LOOPBACK--&T1, &T8
------------------------------------------------------------

This test checks the operation of the modem's transmitter
and receiver.

There are two analog loopback options.  The first, &T1,
involves your typing data that you can verify at your
screen.
The second option, &T8, is an internal self-test that does
not involve the keyboard or screen.  It isolates the modem
from the computer interface to give you a more specific
result.

NOTE:  Dual Standard modems must be set to B0 (default) or
tested at 2400 bps or lower to avoid HST asymmetrical
modulation at higher speeds.
&T1

1.   If you are testing an HST or Dual Standard modem, set
     your computer or software to 2400 bps.

2.   The modem must be in Command mode.  If you wish, set
     Register S18 as a test timer, as explained earlier.

3.   Send the modem the following command.
               AT &M0 &T1 <Enter>

     The modem disables error control, enters analog
     loopback (AL) mode, and sends a CONNECT message.

4.   Type recognizable data so that you can verify it when
     it is looped back to the screen.

5.   End the test.  If you set S18, the modem automatically
     stops the test at the timeout, exits AL mode and
     responds OK.
     
     If you didn't set Register S18, wait one second and
     type +++ to bring the modem back to Command mode.  If
     DIP switch 9 is OFF, the modem also hangs up and ends
     the test.

     If DIP switch 9 is ON, type AT&T0 to end the test.  Or
     send either ATH or the command that resets the modem,
     ATZ.  The latter two commands end the test and hang up
     the modem.  The modem responds OK.  If the modem sends
     an ERROR message, you have issued an invalid command.

6.   If there were no errors, reset the modem to &M4, for
     error control, unless you've issued the ATZ reset
     command.

     NOTE:  If the modem is in online-command mode, that is,
     still connected to a remote modem, and you send it an
     &T1 or &T8 command, it drops the call, enters AL mode,
     sends a CONNECT result and waits for loopback
     characters.

&T8
---
This AL option causes the modem to send an internal test
pattern to its transmitter and loop it back to the receiver.
An internal error detector counts any errors and, when the
test is ended, sends the number of errors or 000 (no errors)
to the screen.

Since you don't type anything during this test, and the
modem does not send anything to the screen, this option
verifies only the modem.  If there are no errors but your
problem continues, it may be at the computer interface.

1.   If you are testing an HST or Dual Standard modem, set
     your computer or software to 2400 bps.

2.   The modem must be in Command mode.  If you wish, set
     Register S18 as a test timer, as explained earlier.

3.   Send the modem the following command:
          AT &M0 &T8 <Enter>

     The modem disables error control and enters AL mode.
     The modem sends its internal test pattern to the trans-
     mitter, and loops the pattern back to the receiver.
     You will not see any data on your screen.

4.   End the test.  If you set S18, the modem automatically
     stops the test at the timeout.  If you didn't set
     Register S18, type AT&T0 to end the test.  Or use ATH
     or the command that resets the modem, ATZ.  Both of the
     latter end the test and hang up the modem.

     The modem hangs up and returns a three-digit code,
     followed by OK.  A code of 000 indicates no errors were
     found.  A code of 255 indicates 255 or more errors.  An
     ERROR message indicates that you issued an invalid
     command.

5.   If there were no errors, reset the modem to &M4 for
     error control unless you issued the ATZ command.

&T2
---
This option is reserved.

DIGITAL LOOPBACK--&T3
------------------------------------------------------------

If your modem has passed the AL test, this test can help you
locate a problem with a remote modem or the telephone
channel.

NOTE:  This test requires the modem to establish a
connection and return to online-command mode in response to
the +++ escape code.  DIP switch 9 must be set ON so that
the modem does not hang up on receipt of the escape code.

After you change the switch, issue ATZ to the modem to
initiate the new setting.

As with AL testing, HST and Dual Standard modems should be
tested at 2400 bps or lower.

1.   Set the modem to &M0, to disable error control.   HST
     and Dual Standard modems should be set to 2400 bps or
     lower to avoid asymmetrical modulation at higher
     speeds.  Establish a connection with the remote modem.

2.   Bring the modem back to Command mode with the +++
     escape code.  Then send it the AT&T3 command.  The
     modem enters DL mode.

3.   The remote user should type a short message.  It will
     be looped back by your modem's transmitter for
     verification on the remote screen.  You will not see
     the message or any other data.

4.   When the remote user has completed the test, issue the
     AT&T0 command to end the test.  Or send either ATH or
     the command that resets the modem, ATZ.  The latter two
     commands end the test and hang up the modem.  The modem
     responds OK.  If the modem sends an ERROR message, you
     have issued an invalid command.

5.   Reset DIP switch 9 OFF if you normally use the factory
     default.  Reset the modem to &M4 unless you used the
     reset command, ATZ.

&T4, &T5
--------
The &T4 option causes the modem to grant a remote modem's
request for a Remote Digital Loopback test.

The &T5 option cancels &T4, and the modem fails to recognize
such a request.  This is the default so that your modem
isn't subject to another user calling and tying up your
modem without your permission.

REMOTE DIGITAL LOOPBACK--&T6, &T7
------------------------------------------------------------

This test, like the local digital loopback test, verifies
the condition of both modems and the phone link.

The request for and granting of Remote Digital Loopback
testing requires that both modems use ITU-T V.22 standard
signaling.  The test must be performed at 2400 bps or lower.
If the remote modem does not have the capability or is not
set to respond, you will get an ERROR result code.

As with Analog Loopback, there are two Remote Digital
Loopback options.  If you select &T6, you send keyboard data
to the modem and verify it when it is returned over the
phone lines and to your screen.  If you select &T7, the
modem sends its internal test pattern and returns an error
count to your screen.

NOTE:  Both test options require the modem to establish a
connection and return to online-command mode in response to
the +++ escape code.  DIP switch 9 must be set ON so that
the modem does not hang up on receipt of the escape code.
If necessary, set the switch ON and then issue the ATZ
command to the modem to initiate the new switch setting.

&T6
---
1.   Set the software to 2400 bps or lower.  Set the modem
     to &M0.  If you wish, set the S18 timer.
     Establish a connection with the remote modem.  If you
     haven't already done so, arrange with the remote user
     to cooperate with your testing and, if necessary, set
     the remote modem to acknowledge the RDL request.  For
     example, older U.S. Robotics high speed modems need to
     be set to S16=8.

2.   Bring the Modem back to Command mode with the +++
     escape code.  Send it the AT&T6 command.  The modem
     enters RDL mode.

3.   Type a short message.  It will be looped back to your
     modem by the remote modem and to your screen for
     verification.  (The remote user will not see your
     data.)

4.   End the test.  If you set Register S18 the modem
     automatically ends the test when the test timeout is
     reached.  If you didn't set S18, type AT&T0 to end the
     test.  Or send either ATH or the command that resets
     the modem, ATZ.  The latter two commands end the test
     and hang up the modem.  The modem responds OK.  If you
     issue an invalid command, the modem sends an ERROR
     message.

     Data errors indicate a problem with the remote modem or
     the phone link.  If you have not performed analog
     loopback testing with your modem, the problem may also
     lie with your modem.

5.   Reset DIP switch 9 OFF unless you normally set that
     switch ON, and issue ATZ to the modem to initiate the
     new setting.  Reset the modem to &M4 unless you used
     the reset command, ATZ.




&T7
---
This test option causes the modem to send an internal test
pattern through the Remote Digital Loopback.  An internal
error detector counts any errors and, when the test is
ended, sends the number of errors or 000 (no errors) to the
screen.

You don't need to type anything during this test.  The modem
sends only its final error count to your screen.

1.   Set the software to 2400 bps or lower.  Set the modem
     to &M0.  If you wish, set the S18 timer.

     Establish a connection with the remote modem.  If you
     haven't already done so, arrange with the remote user
     to cooperate with your testing and, if necessary, set
     the remote modem to acknowledge the RDL request.  For
     example, older U.S. Robotics high speed modems need to
     be set to S16=8.

2.   Bring the modem back to Command mode with the +++
     escape code.  Then send it the AT&T7 command.  The
     modem enters RDL mode.

     The modem sends its internal test pattern to the remote
     modem, which loops it back to your modem.  You will not
     see the data on your screen.

3.   End the test.  If you set S18, the modem automatically
     stops the test when the timer times out.  If you didn't
     set Register S18, type AT&T0 to end the test.  Or send
     either ATH or the command that resets the modem, ATZ.
     The latter two commands end the test and hang up the
     modem.  The modem responds OK.  If you issue an invalid
     command, the modem sends an ERROR message.

     When you terminate the test, the modem returns a three-
     digit code, followed by OK.  A code of 000 indicates no
     errors were found.  A code of 255 indicates 255 or more
     errors.

     If you've performed an Analog Loopback and know your
     modem is working properly, errors indicate a problem
     with either the phone connection or the remote modem.

4.   Reset DIP switch 9 OFF unless you normally operate with
     it ON.  Issue an ATZ command to initiate the new switch
     setting.  Reset the modem to &M4 unless you've sent it
     the ATZ reset command.




TESTING WITH REGISTER S16
------------------------------------------------------------

Register S16 is a bit mapped register with the following bit
functions:

     Bit  Value     Function
     --------------------------
     0    1         Analog Loopback (AL)
     1    2         Dial Test
     2    4         Test Pattern
     3    8         Remote Digital Loopback (RDL)

NOTE:  Earlier U.S. Robotics modems require bit 3 to be
enabled in order to grant RDL to a remote modem.  The modem
now requires its default &T4 setting instead.  To perform
RDL with a U.S. Robotics modem that does not use the &T test
repertoire, that modem should be set to S16=8 before it can
grant RDL testing.

ANALOG LOOPBACK (AL)--S16=1D
------------------------------------------------------------

As with the &T AL test, do not attempt this test under error
control.  HST and Dual Standard modems should be tested at
2400 bps or lower, to avoid asymmetrical modulation at
higher speeds.

To use the modem's Test Pattern (S16, bit 2) instead of
typing your own data, see Test Pattern--S16=4 later in this
appendix.

1.   To initiate testing, type AT&M0S16=1D <Enter>.  The
     modem disables error control, enters AL mode and sends
     a CONNECT result code.

2.   Type data to the modem for the modem to transmit, loop
     to its receiver, and output to the screen.  An
     alternative is to use the Test Pattern, described
     later.

3.   End the test by not typing anything for one second,
     then typing three pluses (+++), and waiting another
     second.  This forces the modem back to Command mode.
     If DIP switch 9 is OFF, the modem exits AL mode and
     returns to Command mode.  If DIP switch 9 is ON, the
     modem maintains the connection when it receives the +++
     escape code.  Issue the ATH command to end AL mode.

4.   Reset the modem to Data mode, S16=0, and error control
     (&M4), or issue the ATZ (reset) command.



Dial Test--S16=2
---------------
The Dial Test is used for factory testing the frequencies of
tone values.  When S-Register 16 is set to 2 and a single
tone is dialed (e.g., ATD7 <Enter>), the modem continues to
transmit that tone until you type another Carriage Return.

Test Pattern--S16=4
------------------
The test pattern can be used instead of your typed data
during Analog Loopback (AL) or Remote Digital Loopback
(RDL), using &T commands or S16.  The test pattern is
available at all speeds.  At 300 bps, the modem's serial
port rate must be fixed (&B1) and the link rate fixed at 300
bps (&N1).  At rates over 9600 bps, just set the modem for a
fixed serial port rate (&B1).

To use the test pattern during AL testing with S16, type the
following command.  The test pattern is sent through the
loopback.
          AT&M0S16=5D <Enter>

To use the test pattern during RDL testing with S16, type
the following command.
          AT&M0S16=12 <Enter>

To use the test pattern with the &T AL or RDL tests, insert
the test pattern command, S16=4, before issuing the test
command.

The first of the following commands initiates AL, the second
RDL:
          ATS16=4&T1 <Enter>
          ATS16=4&T6 <Enter>

The test pattern alone (ATS16=4) is used for testing
equipment and the phone line.  When S16 is set to 4, the
modem transmits the test pattern upon connection with a
remote modem.

Ending Testing with the Test Pattern
------------------------------------
Pressing any character key cancels all test pattern tests
and hangs up the modem.  If you used Register S16, be sure
to reset Register S16 to Data mode when you reset the modem
to its error control defaults, for example, ATZ or
AT&M4S16=0 <Enter>.






REMOTE DIGITAL LOOPBACK--S16=8
------------------------------------------------------------

Responding Modem
----------------
The responding modem must be ready to act on the Courier's
RDL request.  U.S. Robotics high speed modems should be set
to &T4.  If they do not have &T testing capability, they
should be set to S16=8.

Initiating Modem
----------------
1.   If DIP switch 9 is OFF, set it ON so that it does not
     hang up on receipt of the +++ escape code.  Issue an
     ATZ command to initiate the new switch setting.

2.   Set the software to 2400 or 1200 bps.  The ITU-T-
     specified RDL signals are defined only for connections
     at 2400 or 1200 bps.

3.   Disable error control by setting the modem to &M0.
     Then establish a connection with the remote modem.

4.   Bring the modem back to Command mode by sending it the
     escape code:  one second of no data, three pluses
     (+++), and another second of no data.

5.   When the OK result code appears, send the modem the
     following command.
          ATS16=8 O <Enter>

     The modem enters RDL mode (S16=8), and goes back online
     (O command).  Then it transmits the ITU-T-defined RDL
     signals, causing the remote modem to enter RDL mode.

6.   Type any data at the keyboard.  (Or send the test
     pattern.)

7.   To end the test, send the modem the +++ escape code
     again to bring it back to Command mode.

8.   When the modem sends the OK result, reset the modem to
     Data mode with the following command.
          ATS16=0 <Enter>

The modem signals the responding modem that RDL testing is
over.  Terminate the call as you normally would, and reset
the modem to its normal error control setting, &M4 or &M5.
Or, if you wish to resume data transmission with the remote
modem, add the O command to the ATS16=0 string to return the




modem online.  Keep in mind, however, that error control is
disabled.  Because error control is negotiated during the
connection sequence, its status cannot be changed until the
modem is back on hook and in Command mode.


















































+----------------------------------------------------------+
|                                                          |
|   APPENDIX G.  GLOSSARY                                  |
|                                                          |
+----------------------------------------------------------+

Cross-references in the following definitions are enclosed
in quotations.

Analog Loopback
A modem self-test in which data from the keyboard is sent to
the modem's transmitter, modulated into "analog" form,
looped back to the receiver, demodulated into "digital"
form, and returned to the screen for verification.

Analog Signals
Continuous, varying waveforms such as the voice tones car-
ried over phone lines.  Contrast with "digital signals."

Answer Mode
A state in which the modem transmits at the predefined high
frequency of the communications channel and receives at the
low frequency.  The transmit/receive frequencies are the re-
verse of the calling modem which is in "Originate mode."

Application (application program)
A computer program designed to perform a specific function,
such as a word processor or a spreadsheet.

ARQ
Automatic Repeat Request.  A general term for error control
protocols which feature error detection and automatic
retransmission of defective blocks of data.  See "HST,"
"MNP," and "V.42."

ASCII
American Standard Code for Information Interchange.  A 7-bit
binary code (0's, 1's) used to represent letters, numbers,
and special characters such as $, !, and /.  Supported by
almost every computer manufacturer.

Asymmetrical Modulation
A duplex transmission technique which splits the communi-
cations channel into one high speed channel and one slower
channel.  During a call under asymmetrical modulation, the
modem with the greatest amount of data to transmit is allo-
cated the high speed channel.  The modem with less data is
allocated the slow, or back channel (450 bps).  The modems
dynamically reverse the channels during a call if the volume
of data transfer changes.

Asynchronous Transmission
Data transmission in which the length of time between
transmitted "characters" may vary.
Because the time lapses between transmitted characters are
not uniform, the receiving modem must be signaled as to when
the data bits of a character begin and when they end.  The
addition of "Start" and "Stop bits" to each character serves
this purpose.

Auto Answer
A feature in modems enabling them to answer incoming calls
over the phone lines without the use of a telephone
receiver.

Auto Dial
A feature in modems enabling them to dial phone numbers over
the phone system without the use of a telephone transmitter.

Baud Rate
The number of discrete signal events per second occurring on
a communications channel.  Although not technically accu-
rate, baud rate is commonly used to mean "bit rate."

Binary Digit
A 0 or 1, reflecting the use of a binary numbering system
(only two digits).  Used because the computer recognizes
either of two states, OFF or ON.  Shortened form of binary
digit is "bit."

Bit Rate
The number of "binary digits," or bits, transmitted per
second ("BPS").  Communications channels using telephone
channel modems are established at set bit rates, commonly
300, 1200, 2400, 4800, 9600, and 14400.

BPS
The bits ("binary digits") per second rate.

Buffer
A memory area used as temporary storage during input and
output operations.  An example is the modem's command
buffer.  Another is the Transmit Data flow control buffer
used for flow control and to store copies of transmitted
"frames" until they are positively acknowledged by the
receiving modem.

Byte
A group of "binary digits" stored and operated upon as a
unit.  A byte may have a coded value equal to a character in
the ASCII code (letters, numbers), or have some other value
meaningful to the computer.  In user documentation, the term
usually refers to 8-bit units or characters.  1 kilobyte (K)
is equal to 1,024 bytes or characters; 64K indicates 65,536
bytes or characters.

Carrier
A continuous frequency capable of being either modulated or
impressed with another information-carrying signal.
Carriers are  generated and maintained by modems via the
transmission lines of the telephone companies.

CCITT
Formerly, an international organization that defined
standards for telegraphic and telephone equipment.  It has
been incorporated into its parent organization,
International Telecommunication Union ("ITU").
Telecommunication standards are now covered under
Telecommunications Standards Sector (TSS).  ITU-T replaces
CCITT.  For example, the Bell 212A standard for 1200 bps
communication in North America was referred to as CCITT
V.22.  It is now referred to as ITU-T V.22.

Character
A representation, coded in "binary digits," of a letter,
number, or other symbol.

Characters Per Second
A data transfer rate generally estimated from the "bit rate"
and the "character" length.

For example, at 2400 bps, 8-bit characters with "Start" and
"Stop bits" (for a total of ten bits per character) will be
transmitted at a rate of approximately 240 characters per
second (cps).  Some protocols, such as USR-HST and MNP,
employ advanced techniques such as longer transmission
"frames" and "data compression" to increase cps.

Class 1/EIA-578
An American standard used between facsimile application
programs and facsimile modems for sending and receiving
Class 1 faxes.

Class 2.0/EIA-592
An American standard used between facsimile application
programs and facsimile modems for sending and receiving
Class 2.0 faxes.

Cyclic Redundancy Checking (CRC)
An error-detection technique consisting of a cyclic
algorithm performed on each block or "frame" of data by both
sending and receiving modems.  The sending modem inserts the
results of its computation in each data block in the form of
a CRC code.  The receiving modem compares its results with
the received CRC code and responds with either a positive or
negative acknowledgment.  In the ARQ protocol implemented in
U.S. Robotics high speed modems, the receiving modem accepts
no more data until a defective block is received correctly.

Data Communications
A type of communications in which computers are able to
exchange data over an electronic medium.
Data Compression
When the transmitting modem detects redundant units of data,
it recodes them into shorter units of fewer bits.  The
receiving modem then decompresses the redundant data units
before passing them to the receiving computer.

Data Compression Table
A table of values assigned for each character during a call
under data compression.  Default values in the table are
continually altered and built during each call:  the longer
the table, the more efficient throughput gained.

If a destructive Break is sent during a call (see the &Y
command), causing the modems to reset the compression
tables, you can expect diminished throughput.

Data Mode
The mode in which the fax modem is capable of sending and
receiving data files.  A standard modem without fax
capabilities is always in Data mode.

DCE
Data Communication (or Circuit-Terminating) Equipment.  In
this manual, the term applies to dial-up modems that estab-
lish and control the data link via the telephone network.

Dedicated Line
A user-installed telephone line used to connect a specified
number of computers within a limited area, for example, one
building.  The line is a cable rather than a public-access
telephone line.  The communications channel may also be
referred to as nonswitched because calls do not go through
telephone company switching equipment.

Default
Any setting assumed, at startup or reset, by the computer's
software and attached devices, and operational until changed
by the user.

Digital Loopback
A test that checks the send and receive functions between
the modem and computer.  The modem receives data (in the
form of "digital signals") from the computer, and
immediately returns the data to the screen for verification.

Digital Signals
Discrete, uniform signals.  In this manual, the term refers
to the "binary digits" 0 and 1.


Duplex
Indicates a communications channel capable of carrying
signals in both directions. See "Half Duplex," "Full
Duplex."

EIA
Electronic Industries Association, which defines electronic
standards in the U.S.

Equalization
A compensation circuit designed into modems to counteract
certain distortions introduced by the telephone channel.
Two types are used:  fixed (compromise) equalizers and those
that adapt to channel conditions.  U.S. Robotics high speed
modems use adaptive equalization.

Error Control
Various techniques which check the reliability of characters
("parity") or blocks of data.  V.42, MNP and HST error
control protocols use error detection ("CRC") and
retransmission of errored frames ("ARQ").

Facsimile
A method for transmitting the image on a printed page from
one point to another.  Commonly referred to as Fax.

Fax Mode
The mode in which the fax modem is capable of sending and
receiving files in a facsimile format.

Flow Control
A mechanism that compensates for differences in the flow of
data input to and output from a modem or other device.

Frame
A data communications term for a block of data with header
and trailer information attached.  The added information
usually includes a frame number, block size data, error-
check codes, and Start/End indicators.

Full Duplex
Signal flow in both directions at the same time.  In micro-
computer communications, may refer to the suppression of the
online "Local Echo."

Half Duplex
Signal flow in both directions, but only one way at a time.
In microcomputer communications, may refer to activation of
the online "Local Echo," which causes the modem to send a
copy of the  transmitted data to the screen of the sending
computer.

HST
High Speed Technology, U.S. Robotics' proprietary signaling
scheme, design and error control protocol for high-speed
modems.  HST incorporates trellis-coded modulation, for
greater immunity from variable phone line conditions, and
asymmetrical modulation for more efficient use of the phone
channel at speeds of 4800 bps and above.  HST also incorpo-
rates "MNP"-compatible error control procedures adapted to
asymmetrical modulation.

Hz
Hertz, a frequency measurement unit used internationally to
indicate one cycle per second.

ITU-T
International Telecommunication Union-Telecommunication
sector.  Formerly referred to as CCITT.  An international
organization that defines standards for telegraphic and
telephone equipment.  For example, the Bell 212A standard
for 1200 bps communication in North America is observed
internationally as ITU-T V.22.  For 2400 bps communication,
most U.S. manufacturers observe V.22 bis.

LAPM
Link Access Procedure for Modems, an error control
"protocol" incorporated in ITU-T Recommendation V.42.  Like
the "MNP" and "HST" protocols, LAPM uses cyclic redundancy
checking ("CRC") and retransmission of corrupted data
("ARQ") to ensure data reliability.

Local Echo
A modem feature that enables the modem to send copies of
keyboard commands and transmitted data to the screen.  When
the modem is in Command mode (not online to another system)
the local echo is invoked through the ATE1 command.  The
command causes the modem to display your typed commands.
When the modem is online to another system, the local echo
is invoked through the ATF0 command.  This command causes
the modem to display the data it transmits to the remote
system.

MNP
Microcom Networking Protocol, an asynchronous error control
protocol developed by Microcom, Inc. and now in the public
domain.  The protocol ensures error-free transmission
through error detection ("CRC") and retransmission of
errored frames.  U.S. Robotics modems use MNP Levels 1-4 and
Level 5 data compression.  MNP Levels 1-4 have been
incorporated into ITU-T Recommendation V.42.  Compare "HST."

Modem
A device that transmits/receives computer data through a
communications channel such as radio or telephone lines.
The Courier is a telephone channel modem that modulates, or
transforms, "digital signals" from a computer into the
"analog" form that can be carried successfully on a phone
line.  It also demodulates signals received from the phone
line back to digital signals before passing them to the
receiving computer.

Nonvolatile Memory (NVRAM)
User-programmable random access memory whose data is
retained when modem power is turned off.  Used in Courier
modems to store a user-defined default configuration loaded
into random access memory ("RAM") at power on.

OFF/ON Hook
Modem operations which are the equivalent of manually lift-
ing a phone receiver (taking it off hook) and replacing it
(going on hook).

Online Fallback
A feature that allows high speed error-control modems to
monitor line quality and fall back to the next lower speed
if line quality degrades.  The modems fall forward as line
quality improves.

Originate Mode
A state in which the modem transmits at the predefined low
frequency of the communications channel and receives at the
high frequency.  The transmit/receive frequencies are the
reverse of the called modem which is in "Answer mode."

Parallel Transmission
The transfer of data characters using parallel electrical
paths for each bit of the character, for example, 8 paths
for 8-bit characters.  Data is stored in computers in
parallel form, but may be converted to serial form for
certain operations.  See "Serial Transmission."

Parity
An error-detection method that checks the validity of a
transmitted character.  Character checking has been
surpassed by more reliable and efficient forms of block-
checking, including "Xmodem"-type protocols and the "ARQ"
protocol implemented in Courier modems.

The same type of parity must be used by two communicating
computers, or both may omit parity.  When parity is used, a
parity bit is added to each transmitted character.  The
bit's value is 0 or 1, to make the total number of 1's in
the character even or odd, depending on which type of parity
is used.

Protocol
A system of rules and procedures governing communications
between two or more devices.  Protocols vary, but communi-
cating devices  must follow the same protocol in order to
exchange data.  The format of the data, readiness to receive
or send, error detection and error correction are some of
the operations that may be defined in protocols.

RAM
Random Access Memory.  Memory that is available for use when
the modem is turned on, but that clears of all information
when the power is turned off.  The modem's RAM holds the
current operational settings, a flow control "buffer," and a
command buffer.

Remote Access
A feature that allows a remotely-located user to view the
Courier's configuration screens and change the Courier's
configuration.  Password protection is available.

Remote Digital Loopback
A test that checks the phone link and a remote modem's
transmitter and receiver.  Data entered from the keyboard is
transmitted from the initiating modem, received by the
remote modem's receiver, looped through its transmitter, and
returned to the local screen for verification.

Remote Echo
A copy of the data received by the remote system, returned
to the sending system and displayed on the screen.  Remote
echoing is a function of the remote system.

ROM
Read Only Memory.  Permanent memory, not user-programmable.
The Courier's factory settings are stored in ROM and can be
read (loaded) into RAM as an operational configuration if
DIP switch S10 is ON at power on.

Serial Transmission
The transfer of data characters one bit at a time,
sequentially, using a single electrical path.  See "Parallel
Transmission."

Start/Stop Bits
The signaling bits attached to a character before the
character is transmitted during "Asynchronous Transmission."

Terminal
A device whose keyboard and display are used for sending and
receiving data over a communications link.  Differs from a
microcomputer in that it has no internal processing capa-
bilities.  Used to enter data into or retrieve processed
data from a system or network.

Terminal Mode
An operational mode required for microcomputers to transmit
data.  In Terminal mode the computer acts as if it were a
standard terminal such as a teletypewriter, rather than a
data processor.  Keyboard entries go directly to the modem,
whether the entry is a modem command or data to be trans-
mitted over the phone lines.  Received data is output
directly to the screen.  The more popular communications
software products control Terminal mode as well as enable

more complex operations, including file transmission and
saving received files.

Throughput
The amount of actual user data transmitted per second with-
out the overhead of protocol information such as Start and
Stop bits or frame headers and trailers.  Compare
"characters per second."

Transmission Rate
Same as "Bit Rate."

V.21--Fax
An "ITU-T" standard for facsimile operations at 300 bps.
U.S. Robotics or compatible fax devices then transmit or
receive at higher speeds.

V.21--Modem
An "ITU-T" standard for modem communications at 300 bps.
Modems made in the U.S. or Canada follow the Bell 103 stan-
dard.  However, the modem can be set to answer V.21 calls
from overseas.

V.22
An "ITU-T" standard for modem communications at 1200 bps,
compatible with the Bell 212A standard observed in the U.S.
and Canada.

V.22 bis  
An "ITU-T" standard for modem communications at 2400 bps.
The standard includes an automatic link negotiation fallback
to 1200 bps and compatibility with Bell 212A/V.22 modems.

V.23
An "ITU-T" standard for modem communications at 1200 bps
with a 75 bps back channel.  Used in the U.K.

V.25
An "ITU-T" standard for modem communications that specifies
an answer tone different from the Bell answer tone used in
the U.S. and Canada.  All U.S. Robotics modems can be set
with the B0 command so that they use the V.25 2100 Hz tone
when answering overseas calls.

V.27 ter
An "ITU-T" standard for facsimile operations that specifies
modulation at 4800 bps, with fallback to 2400 bps.

V.17
An "ITU-T" standard for facsimile operations that specifies
modulation at 14.4K bps, with fallback to 12K bps.

V.29
An "ITU-T" standard for facsimile operations that specifies
modulation at 9600 bps, with fallback to 7200 bps.

V.32
An "ITU-T" standard for modem communications at 9600 bps and
4800 bps.  V.32 modems fall back to 4800 bps when line
quality is impaired, and fall forward again to 9600 bps when
line quality improves.

V.32 bis
An "ITU-T" standard that extends the V.32 connection range:
4800, 7200, 9600, 12K and 14.4K bps.  V.32 bis modems fall
back to the next lower speed when line quality is impaired,
and fall back further as necessary.  They fall forward to
the next higher speed when line quality improves.

V.42
An "ITU-T" standard for modem communications that defines a
two-stage process of detection and negotiation for LAPM
error control.  V.42 also supports the MNP error control
protocol, levels 1-4.

V.42 bis
An extension of "ITU-T" V.42 that defines a specific data
compression scheme for use with V.42 and MNP error control.

Word Length
The number of bits in a data character without parity, start
or stop bits.

Xmodem
The first of a family of error control software "protocols"
used to transfer files between modems.  These protocols are
in the public domain and are available from many bulletin
board services.

XON/XOFF
Standard "ASCII" control characters used to tell an
intelligent device to stop/resume transmitting data.  In
most systems typing <Ctrl>-S sends the XOFF character.  Some
devices, including the Courier, understand <Ctrl>-Q as XON;
others interpret the pressing of any key after <Ctrl>-S as
XON.












+----------------------------------------------------------+
|                                                          |
|   APPENDIX H.  TECHNICAL SPECIFICATIONS                  |
|                                                          |
+----------------------------------------------------------+

U.S. Robotics V.32 terbo
21.6K, 19.2K, 16.8K, 14.4K. 12K, 9600, 7200 bps
asynchronous,  Trellis Coded Modulation (TCM)
4800 bps, asynchronous, Quadrature Amplitude Modulation
(QAM)

ADDITIONAL COMPATIBILITY FEATURES--DATA MODE
------------------------------------------------------------
ITU-T V.32 bis, 14.4K, 12K, 9600, 7200 bps, asynchronous,
Trellis Coded Modulation (TCM); 4800 bps, asynchronous,
Quadrature Amplitude Modulation (QAM)

ITU-T V.32, 9600 bps, asynchronous, Trellis Coded Modulation
(TCM); 4800 bps, asynchronous, Quadrature Amplitude
Modulation (QAM)

ITU-T V.25 2100 Hz tone

ITU-T V.23, 1200 bps, asymmetrical (1200/75 bps), Frequency
Shift Keying (FSK)

ITU-T V.22 bis, 2400 bps, asynchronous, Quadrature Amplitude
Modulation (QAM)

ITU-T V.22, 1200 bps, asynchronous, Differential Phase Shift
Keying (DPSK)

Bell 212A, 1200 bps, asynchronous, Differential Phase Shift
Keying (DPSK)

Bell 103, 300 bps, asynchronous, Frequency Shift Keying
(FSK)

ITU-T V.21, 300 bps, asynchronous, Frequency Shift Keying
(FSK)

U.S. Robotics HST error control protocol, asymmetrical mode,
at 16.8K, 14.4K, 12K, 9600, 7200, 4800 bps, 450/300 bps back
channel

ITU-T V.42 error control protocol at 14.4K, 12K, 9600, 7200,
4800 bps (V.32 bis mode) and at 2400/1200 bps

ITU-T V.42 bis data compression (all modes and speeds of
1200 bps and higher)

Microcom Networking Protocol (MNP) error control protocol,

Levels 2-4 at 14.4K, 12K, 9600, 7200, 4800 bps (V.32 bis
mode) and at 2400/1200 bps

Microcom Networking Protocol (MNP) Level 5 data compression
(all modes and speeds of 1200 bps and higher)

FAX MODE
------------------------------------------------------------

TIA/EIA-578 Service Class 1 Asynchronous Facsimile DCE
Control Standard

TIA/EIA-592 Service Class 2.0 Asynchronous Facsimile
DCE Control Standard

ITU-T V.17, 14.4K/12K bps

ITU-T V.29, 9600/7200 bps

ITU-T V.27 ter, 4800/2400 bps

ITU-T V.21, 300 bps

U.S. ROBOTICS HIGH SPEED TECHNOLOGY (HST)
------------------------------------------------------------

Dual Standard modems only:
16.8K, 14.4K, 12K, 9600, 7200 bps, asynchronous,
asymmetrical, 450 bps back channel with automatic handshake
adjustment to 300 bps, Trellis Coded Modulation (TCM),
Quadrature Amplitude Modulation (QAM)

4800 bps, asynchronous, asymmetrical, 450 bps back channel
with automatic handshake adjustment to 300 bps, Quadrature
Amplitude Modulation (QAM)

SERIAL PORT RATES
------------------------------------------------------------

115.2K, 57.6K, 38.4K, 19.2K, 9600, 4800, 2400, 1200, 300 bps
Link Rates
Data mode:          V.32 terbo:  21.6K, 19.2K, 16.8K bps
                    HST:  16.8K bps
                    Both:  14.4K, 12K, 9600, 7200, 4800,
                           2400, 1200, 300 bps

Fax mode:           14.4K, 12K, 9600, 7200, 4800, 2400,
                    300 bps

ONLINE FALLBACK/FALL FORWARD
------------------------------------------------------------

21.6K, 19.2K, 16.8K, 14.4K, 12K, 9600, 7200, 4800 bps

PHONE LINE INTERFACE
------------------------------------------------------------

RJ11, RJ45S phone jacks

COMMUNICATIONS CHANNEL
------------------------------------------------------------

Full/half duplex on 2-wire dial-up, dedicated, or leased
phone lines; demand-driven high speed channel turnaround in
HST mode; symmetrical speeds in V.32 modes

OPERATIONAL MODES
------------------------------------------------------------

Asynchronous, Auto Dial/Answer, Manual Originate/Answer,
Smart/Dumb mode, Auto Dial/Auto Answer, Auto Answer only

Fax Modems:  The above modes plus fax mode

FAX SERVICE CLASS 1 COMMANDS
------------------------------------------------------------

+FCLASS=n (0,1)     Class identification and control
+FTS=n (0,255) Stop transmission and pause, 10ms.
+FRS=n (0,255) Wait for silence, 10 ms.
+FTM=n (3,24,48,72,73,74,96,121,122,145,146)
               Transmit data with carrier
+FRM=n (3,24,48,72,73,74,96,121,122,145,146)
               Receive data with carrier
+FTH=n (3,24,48,72,73,74,96,121,122,145,146)
               Transmit HDLC data with carrier
+FRH=n (3,24,48,72,73,74,96,121,122,145,146)
               Receive HDLC data with carrier          

FAX SERVICE CLASS 2.0 COMMANDS
------------------------------------------------------------

Class 2.0 fax commands are too numerous to be listed here.
For information on Class 2.0 technical specifications,
contact Global Engineering Documents, at 1-800-854-7179.
The document that covers this information is:

     ANSI/EIA/TIA-592-1993 (EIA-592)
     Asynchronous Facsimile DCE Control Standard
     May, 1993








Optional Class 2.0 FAX commands supported
-----------------------------------------
U.S. Robotics implements the following optional Class 2.0
fax commands :

+FNS=0,1       Pass-through non-Standard negotiation        
               byte string
+FCR=0,1       Capability to receive
+FAA=0,1       Call Selection mode
+FCT=0-255 sec.     Phase C Timeout
+FHS=0-255          Hang up Status Code, read-only
+FMS=0-3       Minimum Phase C Speed
+FBS?=500,100  Buffer size, read only

DIALING
------------------------------------------------------------

Dialing Rotary (pulse 0-9), Tone (DTMF 0-9, #, *), a-z when
in Quote (") Mode

DATA FORMAT
------------------------------------------------------------

Binary, serial; defaults to 8-bit word length, no parity,
and 1 stop bit

     Word      Parity         Stop
     Length    (1 Bit)        Bits
     ----------------------------------
     7         Even, Odd      1
               Mark, Space
     7         None           2
     8         None           1

FLOW CONTROL BUFFERS
------------------------------------------------------------

Transmit Buffer
     Error control:  3.25k bytes
     Non-Error control:  1.5k bytes, 128-byte option

Receive Buffer:  2K bytes

COMMAND BUFFER
------------------------------------------------------------

40 characters, exclusive of AT prefix, Carriage Return and
spaces






TEST OPTIONS
------------------------------------------------------------

Analog loopback with test pattern
Remote digital loopback
Digital loopback
Test pattern
Dial test

CALL PROGRESS CODES
------------------------------------------------------------

FAX
DATA
NO DIAL TONE
BUSY
NO ANSWER
RINGING
VOICE

FAILED CALL TIMEOUT
------------------------------------------------------------

60-sec. default, programmable 2-255 sec.

ANSWER TONE TIMEOUT
------------------------------------------------------------

60 sec.

ANSWER TONE DETECTOR
------------------------------------------------------------

2200-2300 Hz

LOSS OF CARRIER (DISCONNECT TIMER)
------------------------------------------------------------

0.7-sec. default, programmable 0.2-25.5 sec.

EQUALIZATION
------------------------------------------------------------

Adaptive

TRANSMITTER CARRIER FREQUENCIES
------------------------------------------------------------

USR-V.32 terbo
     Originate Mode:     1800 Hz
     Answer Mode:   1800 Hz
USR-HST, 450 bps back channel
     Originate Mode:     375 Hz
     Answer Mode:   1800 Hz
USR-HST, 300 bps back channel
     Originate Mode:     350 Hz
     Answer Mode:   1800 Hz

V.32 bis
     Originate Mode:     1800 Hz
     Answer Mode:   1800 Hz

V.23
     Originate Mode:     
     Mark:     390 Hz
     Space:    450 Hz
     Answer Mode:
     Mark:     1300 Hz
     Space:    2100 Hz
     
V.22 bis, V.22, Bell 212A
     Originate Mode:     1200 Hz
     Answer Mode:   2400 Hz

Bell 103
     Originate Mode:     
     Mark:     1270 Hz
     Space:    1070 Hz
     Answer Mode:
     Mark:     2225 Hz
     Space:    2025 Hz

V.21
     Originate Mode:
     Mark:     980 Hz
     Space:    1180 Hz
     Answer Mode:   
     Mark:     1650 Hz
     Space:    1850 Hz

RECEIVER CARRIER FREQUENCIES
------------------------------------------------------------

USR-V.32 terbo
     Originate Mode:     1800 Hz
     Answer Mode:   1800 Hz

USR-HST, 450 bps back channel
     Originate Mode:     1800 Hz
     Answer Mode:   375 Hz

USR-HST, 300 bps back channel
     Originate Mode:     1800 Hz
     Answer Mode:   350 Hz




V.32 bis
     Originate Mode:     1800 Hz
     Answer Mode:   1800 Hz

V.23
     Originate Mode:     
     Mark:     1300 Hz
     Space:    2100 Hz
     Answer Mode:
     Mark:     390 Hz
     Space:    450 Hz

     V.22 bis, V.22, Bell 212A
     Originate Mode:     2400 Hz
     Answer Mode:   1200 Hz

Bell 103
     Originate Mode:     
     Mark:     2225 Hz
     Space:    2025 Hz
     Answer Mode:
     Mark:     1270 Hz
     Space:    1070 Hz

V.21
     Originate Mode:
     Mark:     1650 Hz
     Space:    1850 Hz
     Answer Mode:
     Mark:     980 Hz
     Space:    1180 Hz

RECEIVE SENSITIVITY
------------------------------------------------------------

- 44 dBm + 2 dBm


TRANSMIT LEVEL
------------------------------------------------------------

- 9 dBm maximum

TRANSMITTER FREQUENCY TOLERANCE
------------------------------------------------------------
.01%









CERTIFICATION
------------------------------------------------------------

FCC Part 68 and Part 15, Class B Domestic; DOC (Canada), UL
listed

POWER CONSUMPTION
------------------------------------------------------------

5 watts


SIZE
------------------------------------------------------------

6.25 x 10.25 x 1.5 inches
                                                            


















15


