Memory card: Difference between revisions

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JEIDA V3 memory cards used in AES and some [[MVS hardware|MVS systems]] to store game saves and/or high scores. The original SNK card could only hold 2KiB of data.
[[File:snkmemcard.jpg|thumb|SRAM memory card, showing the SRAM chip and voltage detection circuit. Picture by [[User:HPMAN|HPMAN]]]]


Replaced by a 64KiB (?) fixed battery-backed RAM chip in the [[CD hardware|CD systems]].
[[File:NEO-IC8_front.jpg|thumb|NEO-IC8, original SNK card. Picture by [[User:ArcadeTV|ArcadeTV]]]]
[[File:NEO-IC8_back.jpg|thumb|NEO-IC8, back of original SNK card. Picture by [[User:ArcadeTV|ArcadeTV]]]]


See the [[BIOSF_CRDACCESS]] BIOS call description for memory card operations.
The NeoGeo home console and some [[MVS hardware|MVS]] cabs can use [[JEIDA V3]] memory cards to store game saves and/or high scores, allowing players to save their progress and continue on any system running the same game.


[[http://www.neogeoprotos.com/memcardfaq.htm Lots of details (from neogeoprotos.com)]]
Even if the memory card [[68k memory map|address space]] can be freely used, games should only perform memory card operations through the [[CARD]] system ROM call to avoid data corruption.


[[http://www.raregame.ru/file/15/NEO-GEO_Memcard_Data_Format.GIF Data format (from Raregame.ru)]]
=Supported card types=


[[Category:Base system]]
The SP-S2 [[system ROM]] (and probably all the others) can handle 8 memory card sizes from 2KiB up to 16KiB, in 2KiB steps:
*2KiB
*4KiB
*6KiB
*8KiB
*10KiB
*14KiB
*16KiB
 
And 4 different card types:
*8 bits wide
*16 bits wide
*16 bits wide "doubled"
*"SNK ROM" cards
 
For 8-bit cards (all official SNK cards ?) only the lower byte is used, but accesses must '''always''' be done in words. This is because memory card accesses are only enabled for word or upper byte operations (/UDS 68k signal).
 
=Original SNK card=
 
The original SNK-branded memory card was a [[:File:CR2016_battery.jpg|battery-backed]] 8-bit wide 2KiB card using a [[LH5116|LH5116 SRAM chip]] and voltage switching circuitry.
 
Since it uses a battery, it may be prone to data loss if the voltage drops below 2V. Unlike the MVS [[backup RAM]] battery, the memory card one isn't rechargeable.
 
There are at least 2 known versions of the original SNK Memory Card, each with its individual design and circuit-board:<br>
[[Image:NEO-IC8_versions.png|640px]]
 
The first version has the [[C10075-X2-2]] while the later one hase the [[EZ866]] board.
 
=CD systems=
 
A "virtual" memory card is embedded in [[CD systems]] as a 8KiB battery-backed SRAM chip.
 
=Data format=
 
All cards use the same format regardless of capacity, only regions sizes differ. Since the JEIDA data bus is 16-bits wide, make sure to double the address for 8-bit cards if you choose to access their memory directly.
 
The data is referred to as "blocks", one block being 64 bytes. The header always occupies the first block. Eg. A 2KiB card can hold (2048/64)-1 = 31 blocks.
 
The data is split into 5 regions:
 
==Header==
 
Always 64 bytes.
 
{|class="wikitable"
| '''Address'''
| '''Name'''
| '''Size'''
| '''Description'''
|-
|$0~$9
|
|10 bytes
|Zeros or "SNK ROM " (development unit ?)
 
For 16 bits "doubled" cards, $6 is set to $0001
|-
|$A
|CARD_SIZE
|word
|Address space used by the memory card. Eg. A 2KiB 8-bit card is $1000.
|-
|$C
|
|byte
|0
|-
|$D
|CARD_FAT_1_CHKSUM
|byte
|Checksum of FAT 1
|-
|$E
|CARD_FAT_2_CHKSUM
|byte
|Checksum of FAT 2
|-
|$F
|CARD_USERNAME_AVAILABLE
|byte
|0 : Username unavailable, !0 : Username available
|-
|$10
|CARD_USERNAME
|16 bytes
|Card holder's username
|-
|$20
|CARD_MAGIC
|16 bytes
|$4E $XX $45 $XX $4F $XX $2D $XX $47 $XX $45 $XX $4F $XX $80 $XX ("NEO-GEO", $80)
|-
|$30
|CARD_REGION
|byte
|Region of the system that formated the card, 0 = Japan, 1 = USA, 2 = Europe
|}
 
==Directory==
 
List of saves of 32, 64, 96, 128, 160, 192, 224 or 256 entries. The size depends on the card's capacity.
 
Note that since the header occupies the first block, there will always be at least one unused directory entry.
 
Each entry is 4 bytes, with the following format:
 
{| class="regdef"
| '''Address'''
| '''Size'''
| '''Description'''
|-
|$0
|byte
|Save sub-number (CARD_SUB), 0 to 15. $FF if entry is free.
|-
|$1
|word
|Game's [[NGH number]]
|-
|$3
|byte
|FAT entry index (see below)
|}
 
==FAT 1==
 
List of used blocks of 64, 128, 192, or 256 entries. The size depends on the card's capacity.
* $02 is a block reserved by the system ROM
* $01 is a block used by a game
* $00 is a free block
 
==FAT 2==
 
FAT 2 is simply a mirror of FAT 1.
 
If any of the FAT tables checksum is bad, the correct table is written over the other one. If both checksums are bad, the system ROM displays an error.
 
==Game Data==
 
Many games use only one block, but some may use more.
 
The first 20 bytes contain the data title (usually the game and stage name).
 
=Registers=
 
* Write is enabled if {{Reg|REG_CRDUNLOCK1}} and {{Reg|REG_CRDUNLOCK2}} are written to
* The WP (Write Protect) pin is read through bit 6 of {{Reg|REG_STATUS_B}}
* CD1 (Card Detect 1) is read through bit 4 of {{Reg|REG_STATUS_B}}
* CD2 (Card Detect 2) is read through bit 5 of {{Reg|REG_STATUS_B}}
** Both must be 0 if the card is inserted correctly
* Attribute memory is selected if {{Reg|REG_CRDREGSEL}} is written to, never used ?
 
=Pinout=
 
See [[Memory card pinout]].
 
[[Category:Cartridge systems]]

Latest revision as of 01:25, 17 January 2023

SRAM memory card, showing the SRAM chip and voltage detection circuit. Picture by HPMAN
NEO-IC8, original SNK card. Picture by ArcadeTV
NEO-IC8, back of original SNK card. Picture by ArcadeTV

The NeoGeo home console and some MVS cabs can use JEIDA V3 memory cards to store game saves and/or high scores, allowing players to save their progress and continue on any system running the same game.

Even if the memory card address space can be freely used, games should only perform memory card operations through the CARD system ROM call to avoid data corruption.

Supported card types

The SP-S2 system ROM (and probably all the others) can handle 8 memory card sizes from 2KiB up to 16KiB, in 2KiB steps:

  • 2KiB
  • 4KiB
  • 6KiB
  • 8KiB
  • 10KiB
  • 14KiB
  • 16KiB

And 4 different card types:

  • 8 bits wide
  • 16 bits wide
  • 16 bits wide "doubled"
  • "SNK ROM" cards

For 8-bit cards (all official SNK cards ?) only the lower byte is used, but accesses must always be done in words. This is because memory card accesses are only enabled for word or upper byte operations (/UDS 68k signal).

Original SNK card

The original SNK-branded memory card was a battery-backed 8-bit wide 2KiB card using a LH5116 SRAM chip and voltage switching circuitry.

Since it uses a battery, it may be prone to data loss if the voltage drops below 2V. Unlike the MVS backup RAM battery, the memory card one isn't rechargeable.

There are at least 2 known versions of the original SNK Memory Card, each with its individual design and circuit-board:

The first version has the C10075-X2-2 while the later one hase the EZ866 board.

CD systems

A "virtual" memory card is embedded in CD systems as a 8KiB battery-backed SRAM chip.

Data format

All cards use the same format regardless of capacity, only regions sizes differ. Since the JEIDA data bus is 16-bits wide, make sure to double the address for 8-bit cards if you choose to access their memory directly.

The data is referred to as "blocks", one block being 64 bytes. The header always occupies the first block. Eg. A 2KiB card can hold (2048/64)-1 = 31 blocks.

The data is split into 5 regions:

Header

Always 64 bytes.

Address Name Size Description
$0~$9 10 bytes Zeros or "SNK ROM " (development unit ?)

For 16 bits "doubled" cards, $6 is set to $0001

$A CARD_SIZE word Address space used by the memory card. Eg. A 2KiB 8-bit card is $1000.
$C byte 0
$D CARD_FAT_1_CHKSUM byte Checksum of FAT 1
$E CARD_FAT_2_CHKSUM byte Checksum of FAT 2
$F CARD_USERNAME_AVAILABLE byte 0 : Username unavailable, !0 : Username available
$10 CARD_USERNAME 16 bytes Card holder's username
$20 CARD_MAGIC 16 bytes $4E $XX $45 $XX $4F $XX $2D $XX $47 $XX $45 $XX $4F $XX $80 $XX ("NEO-GEO", $80)
$30 CARD_REGION byte Region of the system that formated the card, 0 = Japan, 1 = USA, 2 = Europe

Directory

List of saves of 32, 64, 96, 128, 160, 192, 224 or 256 entries. The size depends on the card's capacity.

Note that since the header occupies the first block, there will always be at least one unused directory entry.

Each entry is 4 bytes, with the following format:

Address Size Description
$0 byte Save sub-number (CARD_SUB), 0 to 15. $FF if entry is free.
$1 word Game's NGH number
$3 byte FAT entry index (see below)

FAT 1

List of used blocks of 64, 128, 192, or 256 entries. The size depends on the card's capacity.

  • $02 is a block reserved by the system ROM
  • $01 is a block used by a game
  • $00 is a free block

FAT 2

FAT 2 is simply a mirror of FAT 1.

If any of the FAT tables checksum is bad, the correct table is written over the other one. If both checksums are bad, the system ROM displays an error.

Game Data

Many games use only one block, but some may use more.

The first 20 bytes contain the data title (usually the game and stage name).

Registers

Pinout

See Memory card pinout.

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