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Modding a NES to run Unisystem VS arcade games (5/14)

Step 3, Additional memory for the CPU

picture of the additional memory The Unisystem VS provides 2KB of additional memory to the CPU. I took the 2KB chip (LH 5216) I removed from the PPU in the previous step and soldered it under under the other CPU memory (U1) by bending all the pins upwards.

The /CE (Chip enable) pin is not soldered since this memory must be accessible from $6000 to $7FFF. Pin #7 of the 74ls139 present on the NES motherboard happends to be low during this range so I connected it to the additional memory's /CE pin.

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Next: Step 4: ROM for the CPU (PRG-ROM) < 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 >

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