Memory card

JEIDA V3 memory cards used in AES and some MVS systems to store game saves and/or high scores. The original SNK card could only hold 2KiB of data.



The official SNK memory card was a battery-based 2KiB card using a LH5116 CMOS SRAM chip and voltage switching circuitry. Data retention voltage: 2V.

The SP-S2 BIOS can handle memory cards up to 16KiB

Replaced by a 8KiB fixed battery-backed RAM chip in the CD systems.

See the CARD BIOS call description for memory card operations.

=Data format=

BIOS can handle 8 different card size (2K, 4K, 6K, 8K, 10K, 14K and 16K) and different card type (8 bits wide, 16 bits wide, 16 bits doubled wide and SNK ROM card).

All the data here are for all the card, it's just a matter on how to read the data between different type of card.

The internal card data are splitted into 5 regions.

Header
Always $80 bytes.

Directory
List of saves. Size depends on card size, it can hold 32, 64, 96, 128, 160, 192, 224 or 256 entries.

Each entry have this format :

FAT 1
List of used blocks. Size depends on card size, it can hold 64, 128 192 or 256 entries. $02 is a BIOS reserved block $01 is a game used block $00 is a free block

FAT 2
FAT 2 is simply a mirror of FAT 1.

Game Data
Normally 64 bytes but maybe some games use more that one block ?

The first 20 bytes are the data title (generally the game name + the stage name).

=Card pinout=