mirror of https://github.com/option8/gp2io.git
28 lines
1.3 KiB
ArmAsm
28 lines
1.3 KiB
ArmAsm
ORG $0300
|
|
ANN0HI EQU $C059
|
|
ANN0LO EQU $C058
|
|
ANN1HI EQU $C05B
|
|
ANN1LO EQU $C05A
|
|
BYTETOSEND EQU $EF
|
|
|
|
SENDBYTE LDY #$08 ; load 8 for a full byte, loop counter
|
|
STA BYTETOSEND ; put byte in zero page for safe keeping
|
|
RTS STA ANN0HI ; annunciator 0 high, RTS
|
|
SENDBIT ROL BYTETOSEND ; rotate byte left, high/MSB out to carry (sendbit)
|
|
BCC SHORTLOOP ; "branch on carry clear" - if carry/bit = 0, goto #311 (short loop)
|
|
LONGLOOP LDX #$14 ; if carry/bit = 1, load X with 20 (long loop)
|
|
JMP SETANN1 ; jump over SHORTLOOP
|
|
SHORTLOOP LDX #$0A ; if carry/bit = 0, load X with 10 (short loop)
|
|
SETANN1 STA ANN1HI ; set annunciator 1 HIGH
|
|
COUNTDOWN DEX ; decrement, countdown to setting ANN1 low (COUNTDOWN)
|
|
BNE COUNTDOWN ; if X > 0, keep counting (goto COUNTDOWN)
|
|
STA ANN1LO ; if done, set ANN1 LOW, countdown to getting next bit
|
|
LDX #$05 ; reset counter for short "reset" transition. This lets the GP2IO stage the bit before the next interrupt
|
|
COUNTDOWN2 DEX ; count down again (COUNTDOWN2)
|
|
BNE COUNTDOWN2 ; if X > 0, keep counting (goto COUNTDOWN2)
|
|
DEY ; decrement y, countdown bits sent
|
|
BNE SENDBIT ; if y > 0, next bit (SENDBIT)
|
|
RTSOFF STA ANN0LO ; annunciator 0 low, sending RTS OFF
|
|
RTS ; return
|
|
|
|
|