PC10 ROM-Images

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Playchoice 10 ROM images can be stored in two formats:

iNES Format

PC10 games in iNES format are indicated by Bit1 of Byte 7 of the iNES header. If the flag is set, then the file should contain some additional entries after the PRG ROM and CHR ROM areas:

  • 8Kbyte INST ROM (containing data and Z80 code for instruction screens)
  • 16 bytes RP5H01 PROM Data output (needed to decrypt the INST ROM)
  • 16 bytes RP5H01 PROM CounterOut output (needed to decrypt the INST ROM) (usually constant: 00,00,00,00,FF,FF,FF,FF,00,00,00,00,FF,FF,FF,FF)

The two required PROM sections are missing in older ROM images. A tool for upgrading such incomplete dumps can be found at http://problemkaputt.de/pc10make.zip

Note: Some very old ROM images don't have the PC10 flag set in the header, and, instead, they declare the 8K INST ROM as an additional CHR ROM bank.

MAME Format

Instead of using a single ROM image file, MAME stores all ROM, EPROM, and PROM chips in separate files.

The PROM data is typically stored in a file called "security.prm". It contains only the 16 Data bytes (not the CounterOut bytes). All bits in the PROM file are inverted, and the bit ordering is reversed: bit0 (the first bit of the PROM's serial bitstream) is stored in bit7 of the 1st byte of the file).

PC10 Emulators

The iNES format is used by no$nes. The MAME format is used by MAME.