> C=Y RM=80 LM=2 TM=1 BM=66 J=NTRS-80 Model 4 HD64180 and Memory Modifications                              > C=NMOD4FIG2/TXT - Updated 01/21/87                                 Fig 2        U58-19 Cas  >-|12|----\                                                       See Note 4.  |  | S08 |11--*---------10|----\                                             *13|----/ OR  |           |LS32 |8--> CAS1x 0-256K  U14-1                        9-U27P    | A18A>--*-9|----/  Note 4. Remove U58 & bend up                             |        |  5-U25P  pin 19 then replace it.         |------------------------|        |     OR   Connect U58-19 to U27P-12&13.   |         |-----------------------|          Then lift U72 bend up pins      |    |----|----|                             12&19 then replace it. They     |----|3a1 1    |                 |----------| connect to nothing.                 | 13-U75P |      |----------|12       1|--> CAS2x  256K-512K          +5 >---|2a0    4a|------|          |         2|--> CAS3x  512K-768K                 | 74LS157 | A20 U37P-2  >---|13       3|--> CAS4x  768K-1024K         Gnd>-15|---------| A19 U37P-19 >---|14       4|--> CAS5x  1024K-1280K                                           |  74LS42 5|--> CAS6x  1280K-1536K                        |-------|          |12-U76P  6|--> CAS7x  1536K-1792K        AD18 U37P-16  >-|2a0  a4|----------|15       7|--> CAS8x  1792K-2048K        A18A U35P-12  >-|3a1    |          |         9|      Unused                                  |13-U63P|          |        10|      Unused                                  |74LS157|          |        11|      Unused                  Z80/MMU U41P-11>|1      |          |----------|                               ___            |-------|                       ___                           REF >---------2|----\                  ____    REF >----9|----\             _____           | S08 |3---> Ram Bank 1 CAS1              | S08 |8---> Ram   CAS1x >--------1|----/        See Note 4.      CAS2x >--10|----/  Bank 2                    10-U14P    Cas1&2 connect to the feed      9-U27P    ____      ___              AND     holes just below the ram banks    AND     CAS2      REF >---------4|----\    that went to U72 12&19                ____         _____           | S08 |6---------------------------> Ram Bank 3 CAS3         CAS3x >--------5|----/                                                                      14-U46P   Note: Cut Traces for Cas lines at the feed hole      ___              AND    just below the ram banks going to U72 if the rams    REF >---------1|----\   appear to be unstable    ____                       _____           | S08 |3-------------> Ram Bank 3 CAS4                       CAS4x >--------2|----/                                                      -----------------------------------------------------------------------      >C=YWrite Protect for Ram Based Operation - 0 to 14K>C=N                                             Tandy Mod-This Res. is not on     U55-9 A14 >------1|                   __            the Sch.   56 Ohm        U55-18 A15 >-----2|----\              WR All 256K Rams <-----/\/\/\---|      U35P-4 A16 >-----3| S260|5-----------------1|----\            R63     |      U35P-7 A17 >----12|----/         |---------2| S11 |12----13|----\     |      U14P-9 A18-A20 >13| 15-U29P      |    |---13|----/         |LS32 |11--|                          NOR          |    |    16-U31P     |-12|----/   R63                                       |    |       AND      |   7-U39P  Memory    U72-6 Fxupmem >--4|              |    |                |     OR    Write     U25P-6 MB1&0 >-- 8|----\         |    |                |           For Rams           *-------9| S260|6-------|    |------|         |---------|                    *------10|----/                     |            ___    |                    *------11| 15-U29P   U59-2 SEL0 >---|     U38-11 MWR >--|                    |          NOR                         Note 5.                               |------------------------------------|   Find Resistor on back of                                                 | main board between U38-11                          | \                     | and R63. Remove and mount                          |   \                   | on the front side with       U37P-6 Write  >------5| S04 O-----------------| above connections.                  Protect Bit    |   /  6     the 56 Ohm                                       D6             | / 17-U61P  resistor                                 