C64 Cartridge formats – “Ocean”

“Ocean” Game Cartridges

“Type A” (up to 256k):

  • 128k Batman
  • 128k Battle Command
  • 128k Double Dragon
  • 128k Navy Seals
  • 128k Pang
  • 128k Robocop 3
  • 128k Toki
  • 256k Chase H.Q. II
  • 256k Robocop 2
  • 256k Shadow of the Beast
  • 256k Space Gun

“Type B” (512k):

  • 512k Terminator 2

Note: other sizes (such as 32k) exist in the wild as crt files, but these do not seem to be official ocean cartridges.

“Type A” cartridges work like this:

  • the hardware uses 16k game config, the same 8k ROM bank is mapped to both ROML and ROMH.
  • the software accesses banks 0-15 at ROML ($8000-$9FFF) and banks 16-31 at ROMH ($A000-$BFFF) (only 256k type)

“Type B” cartridges work like this:

  • the hardware uses 8k game config, 8k ROM bank is mapped to ROML.
  • the software accesses banks 0-63 at ROML ($8000-$9FFF).

Note: a generic implementation may always use 16k game config and mirror the ROM banks (the terminator2 cart will work with it).

Bank switching is done by writing to $DE00. The lower six bits give the bank number (ranging from 0-63). Bit 7 in this selection word is always set (but has no effect).

November 18th, 2022 | Posted in Commodore 64 |

Comments are closed.