Displaying text

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ASM routine for displaying text with a 8x8 pixel font on the fix layer:

;Displays text pointed by A0 at the VRAM address in D1. $FF:Next line, $00:End of text.
;Uses A0, D0 and REG_VRAMMOD. ASCIISTART is the character 0 fix tile.
Write8Text:
    move.w  d1,REG_VRAMADDR
    move.w  #$20,REG_VRAMMOD
.textmaplp:
    clr.w   d0
    move.b  (a0)+,d0
    tst.b   d0
    beq     .textmapend
    cmp.b   #$FF,d0
    bne     .nolinejump
    addq.w  #1,d1
    move.w  d1,REG_VRAMADDR
    bra     .textmaplp
.nolinejump:
    addq.w  ASCIISTART,d0
    move.w  d0,REG_VRAMRW
    bra     .textmaplp
.textmapend:
    rts

"ASCIISTART" should be the fix tile number corresponding to ASCII value 0. This depends on what tileset you are using. Usually, onboard fix tilesets have a full 8x8 font starting at tile #0.

The VRAM address is calculated from the desired text position: D1=#FIXMAP+(Y+2+((X+1)*32)), "FIXMAP" being #$7000.