Apple2-IO-RPi/Firmware/test.asm

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ldx #$50 ;slot 5 for this test
start: lda #$80 ;set read flag low (ready to read)
sta $c08d,x ;bit 1 low for writing values
waitwl: lda $c08e,x ;bit 0 low for reading values
bmi waitwl ;wait for write flag low
jsr $fde3 ;print nibble of data
lda #$c0 ;set read flag high (done reading)
sta $c08d,x
waitwh: lda $c08e,x
bpl waitwh ;wait for write flag high
bmi start ;go around againg for next nibble