80 lines
2.5 KiB
Plaintext
80 lines
2.5 KiB
Plaintext
;*** POKE80
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;*** STORES ANY BYTE DIRECTLY ON 80 COLUMN SCREEN
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;*** USING PROTOCOL DESCRIBED IN "INSIDE THE APPLE //E"
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;--------
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; POKE80
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;--------
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; A = CHARACTER TO POKE ON SCREEN
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; X = X COORDINATE (0-79)
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; Y = Y COORDINATE (0-23)
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;--------
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POKE80 CPX #80 ;VALIDATE X,Y COORDINATES
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BCC POKE80A
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CPY #24
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BCC POKE80A
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RTS
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POKE80A PHP ;SAVE INTERRUPT STATUS
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PHA ;SAVE USER'S DATA BYTE
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STA SAVEA
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STX SAVEX
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STY SAVEY
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SEI ;DISABLE INTERRUPTS
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LDA $C018
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STA STAT80ST ;SAVE STATUS OF 80STORE AND PAGE2 FLAGS
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LDA $C01C
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STA STATPAG2
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STA $C001 ;TURN 80STORE ON TO USE PAGE2 TO SWITCH MAIN->AUX
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LDA $28
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STA SAVEBASL ;SAVE CURRENT SCREEN BASE ADDRESS
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LDA $29
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STA SAVEBASH
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TYA ;MULTIPLY Y BY 2 FOR LOOKUP IN BASE TABLE
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ASL A
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TAY
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LDA BASTABLE,Y ;GET LINE ADDRESS AND STORE IT IN ZP VECTOR
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STA $28
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INY
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LDA BASTABLE,Y
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STA $29
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TXA ;DIVIDE X BY 2 TO GET OFFSET FROM LINE BASE
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LSR A
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TAY ;PUT IT IN Y FOR THE INDIRECT ADDRESSING LATER
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BCC EVENCOL ;CHECK CARRY TO DETERMINE IF X WAS ODD OR EVEN
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STA $C054 ;ODD - TURN PAGE 2 OFF
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BCS STORBYTE
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EVENCOL STA $C055 ;EVEN - TURN PAGE 2 ON
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STORBYTE PLA
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STA ($28),Y ;POKE THE CHARACTER ON THE SCREEN
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LDA STAT80ST
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BPL OFF80ST
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STA $C001 ;80STOREON
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BMI RSTRPAG2
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OFF80ST STA $C000 ;80STOREOFF
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RSTRPAG2 LDA STATPAG2
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BPL OFFPAG2
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STA $C055 ;PAGE2ON
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BMI RSTRBASE
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OFFPAG2 STA $C054 ;PAGE2OFF
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RSTRBASE LDA SAVEBASL ;RESTORE ZP BASE VECTOR
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STA $28
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LDA SAVEBASH
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STA $29
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LDX SAVEX
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LDY SAVEY
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LDA SAVEA
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PLP ;RESTORE INTERRUPT STATUS
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RTS
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;
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STAT80ST DFB $00
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STATPAG2 DFB $00
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SAVEBASL DFB $00
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SAVEBASH DFB $00
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SAVEA DFB $00
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SAVEX DFB $00
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SAVEY DFB $00
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BASTABLE DFB $00,$04,$80,$04,$00,$05,$80,$05,$00,$06,$80,$06,$00,$07,$80,$07
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DFB $28,$04,$A8,$04,$28,$05,$A8,$05,$28,$06,$A8,$06,$28,$07,$A8,$07
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DFB $50,$04,$D0,$04,$50,$05,$D0,$05,$50,$06,$D0,$06,$50,$07,$D0,$07
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;
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CHN MFF0DRVR.SC4
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