Displaying credits: Difference between revisions

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(Created page with "The system ROM takes care of displaying the credits on the LED displays itself (see MV-LED board). The credit count for each player is stored in $D00034 for player 1,...")
 
m (Removed BCD conversion)
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The [[system ROM]] takes care of displaying the credits on the LED displays itself (see [[MV-LED]] board).
The [[system ROM]] takes care of displaying the credits on the LED displays itself (see [[MV-LED]] board).
The credit count for each player is stored 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.


It's up to the game to display the counts on the screen when needed. SNK recommends using a 8x8 [[fix layer]] font.
It's up to the game to display the counts on the screen when needed. SNK recommends using a 8x8 [[fix layer]] font.


Hex to BCD conversion (untested):
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.
<syntaxhighlight>
moveq.l #0,d0        ; Clear D0
move.b  $D00034,d0  ; Read P1 credits (hex)
move.w  d0,d1        ; Make a copy
divu.w  #10,d0      ; Credits / 10
swap    d0          ; Take care of remainder first
sub.b  d1,d0        ; Get units
move.b  d0,d1
andi.b  #$0F,d1      ; Mask off tens
swap    d0          ; Go back to quotient
lsl.b  #4,d0        ; Shift tens to left digit
or.b    d1,d0        ; Mix tens and units
</syntaxhighlight>


If $0C is in $D00034 we get $12, which is $0C in decimal but stored as hex. It's now trivial to get fix tile numbers for display on the fix layer.
'''Note''': [[SYSTEM_IO]] must be called each v-blank to update those locations.


<syntaxhighlight>
<syntaxhighlight>
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  #$7088,REG_VRAMADDR    ; Set position in fix map, top left
move.w  d0,d1                  ; Make a copy of the BCD value
move.w  d0,d1                  ; Make a copy of the BCD value

Revision as of 03:41, 6 October 2017

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
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