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https://github.com/nippur72/apple1-videocard-lib.git
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23 lines
1.1 KiB
C
23 lines
1.1 KiB
C
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#include <utils.h>
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#include <apple1.h>
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byte *const LASTSTATE = 0x29; // Last input state
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byte *const TAPEIN = 0xC081; // Tape input
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byte *const DSP = 0xD012; // display data port
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void main()
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{
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asm {
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simple_monitor: lda TAPEIN // read tape input
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cmp LASTSTATE // compare to previous state
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beq no_toggle // if same just skip
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sta LASTSTATE // else save new state
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ldx #35 // set "toggle detected" flag in X, 35 is also the char to print
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no_toggle: bit DSP // check if display is ready to accept a character
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bmi simple_monitor // if not, just keep reading tape
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stx DSP // else display the "toggle detected" flag character
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ldx #45 // resets the "toggle detected" flag to the "-" sign, sets also Z=0 flag
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bne simple_monitor // cheap jump because Z is also 0
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}
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}
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