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    AST RESEARCH, INC.              TECHNICAL BULLETIN # 0949       7-19-94

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       WINDOWS FOR WORKGROUPS AND PENTIUM(TM)-BASED SYSTEMS WITH A 16550 UART CHIP

    PROBLEM:        When using Windows for Workgroups version 3.11 with serial
                    communications software, the following problems may occur:

                    1- Using a Pentium(TM)-based machine with a 16550 UART chip,
                       when the serial communications application attempts to open
                       the communications port, the system may stop responding
                       (hangs) if there is data in the chip.

                    2- When using communications software, one connection may be
                       possible after starting Windows for Workgroups, but any
                       subsequent connections may fail and may hang the system.
                       While this does not normally cause problems, the second
                       connection may fail with some modems.

    CAUSE:          1- A problem with the 16550 UART implementation causes the chip
                       to become trapped in a mode in which data is always
                       detected in its FIFO buffer.

                    2- This problem occurs when SERIAL.386 sends an extra NUL
                       character through the port, when the communications
                       software calls the CloseComm Application Program Interface
                       (API) function.

    SYSTEMS
    AFFECTED:       All Pentium(TM)-based systems with a 16550 UART chip.

    SOLUTION:       Download the SERIAL.EXE file from AST’s BBS and copy it onto a
                    diskette.  This WG1001 file contains an updated SERIAL.386
                    driver that corrects both problems.

                    To install the updated SERIAL.386 file do the following:

                    1. Quit Windows for Workgroups.

                    2. Make a backup copy of the currently installed SERIAL.386
                       file by typing the following at the MS-DOS command prompt
                       and then pressing :

                               ren :\serial.386 serial.old

                       where : is the location of your Windows SYSTEM
                       subdirectory.

                       For example, if your Windows directory is called WINDOWS and
                       it is on drive C, type the following at the MS-DOS command
                       prompt and then press :

                               ren c:\windows\system\serial.386 serial.old

                    3. Insert the WG1001 file in the appropriate floppy disk drive.

                    4. To copy the file to the Windows SYSTEM subdirectory, type
                       the following at the MS-DOS command prompt and then press
                       :

                               copy :\serial.386 :

                       where  is the floppy disk drive containing the WG1001
                       file and  is the drive and directory of your
                       Windows SYSTEM subdirectory.

                       For example, if the WG1001 file is in drive A and your
                       Windows directory is called WINDOWS, and it is on drive C,
                       type the following at the MS-DOS command prompt and then
                       press ENTER:

                               copy a:\serial.386 c:\windows\system