NES-CPROM

Cartridge Board

What Is It?

A discrete logic Nintendo-made board.
Max 32K of PRG ROM
16K VRAM
74161, 7404, 7408.
Note: this board has bus conflicts.

The Tech:

The LS161 acts as a latch. It latches D0 and D1. Writing anywhere in the 8000h- FFFFh range will set this latch using the above data lines.

The VRAM is broken up into 4, 4K banks. The PPU space is thusly broken up into 2 4K banks. The lower 4K bank is fixed to the first VRAM page. The upper 4K bank is movable.

7  bit  0
---- ----
xxxx xxCC

The C bits select a 4K VRAM bank for the upper half of PPU space.

Mirroring is hardwired on the cart.