ShopModding a NES to run Unisystem VS arcade games (4/14)
Step 2: Additional memory for the PPU
As I explained previously, 4KB of memory must be available to the PPU instead
of 2KB. The memory chip (U4) must be replaced by a bigger one.
The pinout uesd by different memory chips is usually similar. This allows us to solder the bigger chip where the small one was, with a minimal number of wires and bent pins. The additional address line A11 must be connected to PPU pin #27. If you use a memory chip bigger than 4K, connect all the remaining address pins (A12 and higher) to VCC or ground.
On an old 486 motherboard, I found an As7c256 32K
sram chip. To make sure I did not make mistakes, I drew a small diagram to compare
the pinout of the 2K memory chip (LH5216) with this new chip.
The pinout uesd by different memory chips is usually similar. This allows us to solder the bigger chip where the small one was, with a minimal number of wires and bent pins. The additional address line A11 must be connected to PPU pin #27. If you use a memory chip bigger than 4K, connect all the remaining address pins (A12 and higher) to VCC or ground.
On an old 486 motherboard, I found an As7c256 32K
sram chip. To make sure I did not make mistakes, I drew a small diagram to compare
the pinout of the 2K memory chip (LH5216) with this new chip.
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