CPROM

NES-CPROM (no HVC-CPROM known) is a particular Nintendo cartridge board which uses discrete logic to provide up to four 4 KB banks of CHR RAM. The iNES format assigns mapper 13 to this board. Only Videomation, a paint program for NES, is known to use it.

Overview

• PRG ROM size: 32 KB (DIP-28 standard pinout)
• PRG ROM bank size: Not bankswitched
• PRG RAM: None
• CHR capacity: 16 KB RAM
• CHR bank size: 4 KB
• Nametable mirroring: Vertical
• Subject to bus conflicts: Yes

Banks

• PPU $0000-$0FFF: 4 KB fixed CHR RAM bank (first page)
• PPU $1000-$1FFF: 4 KB swappable CHR RAM page

Registers

Bank select ($8000-$FFFF)

7  bit  0
---- ----
xxxx xxCC
       ||
       ++- Select 4 KB CHR RAM bank for PPU $1000-$1FFF

Hardware

The CPROM board uses a 74HC161 (4-bit latch), 74HC04 (hex inverter), and 74HC08 (quad 2-input AND gate).