Displaying credits: Difference between revisions
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Revision as of 17:00, 27 January 2018
The system ROM takes care of displaying the credits on the LED displays itself (see MV-LED board).
It's up to the game to display the counts on the screen when needed. SNK recommends using a 8x8 fix layer font.
The credit count for each player is stored in BCD in $D00034 for player 1, and $D00035 for player 2. These locations are in the backup RAM, to keep the credit counts in case of a power failure during play.
Note: SYSTEM_IO must be called each v-blank to update those locations.
moveq.l #0,d0
move.b $D00034,d0 ; Read P1 credits (hex)
move.w #$7088,REG_VRAMADDR ; Set position in fix map, top left
move.w d0,d1 ; Make a copy of the BCD value
move.w #$20,REG_VRAMMOD ; Auto-inc fix column
lsr.b #4,d1 ; Get tens
andi.w #$000F,d1 ; Mask off eventual garbage
ori.w #$5030,d1 ; Set palette 5 and tile offset $30 (ASCII "0")
move.w d1,REG_VRAMRW ; Write tens to VRAM
andi.w #$000F,d0 ; Get units
ori.w #$5030,d1 ; Same
move.w d1,REG_VRAMRW ; Write units to VRAM