4-in-1 multicart

4-in-1 multicart

4-in-1 menu

4-in-1 top

4-in-1 bottom

4-in-1 schematic

This cartridge contains 4 CNROM games:

• Puzzle
• F-15 City War
• Volley Ball
• PokeBlock

CPU banks

$8000-$ffff: 32 kB ROM bank (swapppable)

PPU banks

$0000-$1fff: 8 kB ROM bank (swappable)

Mirroring

H/V (selected by software)

Subject to bus conflicts

Yes

Registers

$8000-$ffff: PRG/CHR bank selection register

7      0
--------
xxPPCCCC
  ||||||
  ||++++- select 8kB CHR-ROM bank at $0000-$1fff
  ++----- select 32 kB PRG-ROM bank at $8000-$ffff
  +------ select mirroring (0=H, 1=V)

Quirks

• Multicart register overlaps CNROM register and multicart register is not protected from writes after game is selected, so all games CHR-bank switching rougines had to be patched.
• The register is not initialized on startup so reset vector of all games had to be patched
• DIP28 1 MB mask roms are used both for PRG and CHR (pin 22, which is normally used as !OE in DIP28 EEPROMS is utilized as A16)