23 lines
608 B
ArmAsm
23 lines
608 B
ArmAsm
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;;
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;; Wait 1 ms (1000 usec) - afterwards can use 'bpl' to check that DATA is pulled
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;;
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;; On NTSC this means 1023 cycles (slightly less on PAL, but we have to be sure).
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;; We can't count on badlines, as the screen might be disabled.
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;; Delay here is implemeented using VIC-II raster register. Since one raster is
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;; 63 cycles, we need at least 17 full rasters to be 100% sure we wait enough
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iec_wait1ms_for_data:
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ldx #18 ; we probably won't start with the beginning of raster
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lda VIC_RASTER
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*
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cmp VIC_RASTER
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beq -
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lda VIC_RASTER
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dex
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bne -
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lda CIA2_PRA ; pulled DATA = highest bit 0 = 'plus'
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rts
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