> C=Y RM=80 LM=2 TM=1 BM=66 J=NTRS-80 Model 4 HD64180 and Memory Modification> C=NMOD4FIG3/TXT - Updated 01/21/87                               Fig 3                                                                                                     Address Mapping Defeat                                                                                                                      A16 U35P-3  >---1|----\                                                                       | S32  |3--------4|----\                                    A17 U35P-6  >---2|----/            | S32  |6-------1|----\                                   18-U20P       |---5|----/           | S08  |3-----|          HDA18 U35P-13 >---------------|   18-U20P     |----2|-----/       |                                                        |    9-U27P         |          Z80/HD U37P-9 >-------------------------------|                   |                                                                            |                                     |--------------------------------------|           If we could replace U37&59| with a faster PAL or 74F logic  then we could   U37-12 >-------------------|-----9|----\     Run at 6.0 Mhz or faster                                   |      | S32  |8------------> U31P-13               Lift U37 bend up Pins    |----10|----/                  Sel 0                12&15 then replace it.   |     18-U20P                                       Connect to U20P          |----12|----\                                                                       | S32  |11-----------> U59-1               U37-15 >------------------------13|----/                  Sel 1                                                             Note : Remove U59 then                  This circuit will disable address           bend up Pins 1&2               decode when the MMU is accessing memory       on U59 and Replace it.         beyond the normal 64K map.                                            