Controlling the credits display
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To display the credits on-screen, see displaying credits.
You should let the system ROM be in charge of controlling the credits displays. But if you want to try things, here's how it goes:
See the bit definitions of the REG_LEDDATA and REG_LEDLATCHES registers for more details.
The system ROM uses ~35us delays done with fall-through calls to NOPs.
Credits for P1 are in D0, for P2 in D1.
move.b #$FF, REG_LEDLATCHES ; Set clock high
jsr wait
not.b d0 ; The digits are sent inverted
move.b d0, REG_LEDDATA ; Set digits
move.b #$EF, REG_LEDLATCHES ; Set clock low (latch P1 digits)
jsr wait
move.b #$FF, REG_LEDLATCHES ; Set clock back high
jsr wait
not.b d1 ; The digits are sent inverted
move.b d1, REG_LEDDATA ; Set digits
move.b #$DF, REG_LEDLATCHES ; Set clock low (latch P2 digits)
jsr wait
move.b #$FF, REG_LEDLATCHES ; Set clock back highwait:
movem.l d0-d7/a0-a5,-(a7) ; 120 cycles
movem.l (a7)+,d0-d7/a0-a5 ; 124 cycles
movem.l d0-d7/a0-a5,-(a7) ; 120 cycles
movem.l (a7)+,d0-d7/a0-a5 ; 124 cycles, total = 488 cycles = 40.7us
rts