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January 6, 2017 16:31
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| Get_Keys:: | |
| ld a,$20 | |
| ld [$ff00],a ; set bit 5 low to enable buttons | |
| ld a,[$ff00] ; allow time for it to bounce | |
| ld a,[$ff00] ; get result | |
| cpl ; invert (because a low result means the button is pressed) | |
| and $0f ; throw out high nybble | |
| swap a | |
| ld b,a ; save low nybble as high nybble of b | |
| ld a,$10 | |
| ld [$ff00],a ; set bit 4 low to enable dpad | |
| ld a,[$ff00] ; allow time for it to bounce | |
| ld a,[$ff00] ; (i don't know why i allow so much more time for this to | |
| ld a,[$ff00] ; bounce than the buttons, but all the example code i've seen | |
| ld a,[$ff00] ; does it) | |
| ld a,[$ff00] | |
| ld a,[$ff00] ; get result | |
| cpl ; invert again | |
| and $0f ; throw out high nybble | |
| or b ; combine the two nybbles into one byte | |
| ld b,a ; save it in b | |
| ld a,$30 | |
| ld [$ff00],a ; reset joypad register | |
| ret |
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