Backup RAM

The backup RAM is a battery-powered 64KiB RAM space used by MVS systems to store game scores, cab infos and income logs. Access is handled by the BIOSes.

Memory region: $D00000~$D0FFFF (Mirrored up to $DFFFFF ?).

Data structure
All offset are taken from the sp-s2.bin bios.


 * $D00000~$D0000F: Nothing ($00)
 * $D00010: "BACKUP RAM OK !",$80
 * $D00020.l: ?
 * $D00021.b: btst 0,1,2,3,4
 * $D00024.l: adresse ?
 * $D00034.l: adresse ?
 * $D00038.w: ? bit 4 tst
 * $D0003A: Start of ? (13 bytes)
 * $D00042.b: tst ?
 * $D00043.b: tst ?
 * $D00044.w: ?
 * $D00046.b: SOUND_STOP, No sound at all if non-zero
 * $D00047.b: Number of detected slots
 * $D00048.l: ?
 * $D0004C.b: ? ($3B)
 * $D00058.b: First valid slot
 * $D0005E.b: Something to do with tested slot? tst
 * $D0005A.b: heure ?
 * $D00060.w: multi-slot flag
 * $D00104: year,month,day ? (3 bytes) Modify date
 * $D00108.b: Selected tested slot
 * $D00109.b: Compared with 8
 * $D0011A: Start of ?
 * $D00122.b: ? ($23)
 * $D00124: adresses ? (4 bytes * nb of slots ?)
 * $D00144: Date (Year, Month, Day, ? *8 ?) Creation date
 * $D001AC.l: $F0F0F0F0
 * $D001B0.w: $FFFF


 * $D002A0: Title of game (16 bytes *8 ?)


 * $D00320: ?