Version 1 'final' demo for the Apple II'

DEMO.ASM

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+.ORG $8000
+
+CLOBBER:
+LDA #$04 ; text / lo mem address
+STA $0B
+LDA #$00 ; text / lo mem address
+STA $0A
+LDA #$60 ; graphic asset address
+STA $0D
+LDA #$00 ; graphic asset address
+STA $0C
+
+CLOBNP:
+LDY #$00 ; indirect addressing mode stuff
+CLOBLOOP:
+LDA ($0C),y
+STA ($0A),y
+INY
+CPY #$FF
+BNE CLOBLOOP
+LDY $0B
+INY
+STY $0B
+CPY #$20
+BEQ TIMER
+LDY $0D
+INY
+STY $0D
+JMP CLOBNP
+
+TIMER:
+LDY #$00
+STY $71 ; timer1 y
+OUTERLOOP:
+LDY $71
+LDX #$00
+STX $70 ; timer1 x
+INNERLOOP:
+LDX $70
+INX
+STX $70
+CPX #$FF
+BNE INNERLOOP
+INY
+STY $71
+CPY #$FF
+BNE OUTERLOOP
+JSR LGRMODE
+JMP TIMER2
+
+TIMER2:
+LDY #$00
+OUTERLOOP2:
+LDX #$00
+INNERLOOP2:
+INX
+CPX #$FF
+BNE INNERLOOP2
+INY
+CPY #$FF
+BNE OUTERLOOP2
+JSR INITDISPLAY
+
+LGRMODE:
+LDA #$FF
+STA $C056
+STA $C054
+STA $C050
+RTS
+
+INITDISPLAY:
+LDA #$FF
+STA $C057
+STA $C054
+STA $C050
+LDA #$80
+STA $2000
+STA $2001
+STA $2002
+STA $2003
+JMP XOREFFECT
+
+LOADBUFFER:
+LDA #$FF
+LDX #$00
+LOADLOOP:
+STA $20,x
+INX
+CPX #$28
+BNE LOADLOOP
+JMP GLITCHINIT
+LOOP:
+NOP
+JMP LOOP
+
+XOREFFECT:
+LDA #$34
+STA $01 ; start memory address
+LDA #$25
+STA $02 ; width of individual row
+LDA $01
+ADC $02
+STA $03 ; memory address of end of line
+LDA #$00
+STA $64 ; counter 1
+STA $65 ; counter 2
+STA $66 ; counter 3
+LDA $00
+STA $08 ; low order address byte
+LDA $20
+STA $09 ; high order address byte
+GLITCHINIT:
+LDX #$65
+STX $04 ; memory address currently being grabbed
+GLITCHSTORE:
+;LDA $2000,x ; grab the byte from HGR memory
+LDA #$FF
+STA $20,x ; store it in zero page
+INX
+STX $04 ; store current memory address
+TXA
+CMP $02
+BNE GLITCHSTORE
+LTIMERY:
+LDA #$00
+STA $65
+LTIMERX:
+LDA #$00
+STA $64
+XEINIT:
+LDX $01
+XELINE:
+LDA $2000,x
+EOR $20,x
+STA $2000,x
+INX
+STX $04 ; store current XOR byte
+TXA
+CMP $02 ; compare to width of row
+BNE XELINE
+LTIMER:
+LDX $64 ; start of long timer
+INX
+STX $64
+CPX #$FF
+BNE XEINIT
+LDX $65
+INX
+STX $65
+CPX #$02
+BNE LTIMERX
+LDA #$FF ; switch to page 2
+STA $C050
+STA $C052
+STA $C057
+STA $C055
+; go through once more in the timer
+LDA #$00
+STA $64
+STA $65
+LDX $66
+INX
+CPX #$02
+BEQ CLEANUP
+
+;LDX $66 ; don't need this third variable
+;INX
+;STX $66
+;CPX #$FF
+;BNE LTIMERY
+;JMP XEINIT
+
+;SWITCHPAGE:
+;LDA #$FF
+;STA $C055
+;RTS
+
+CLEANUP:
+LDA #$00
+STA $4000
+STA $4001
+STA $4002
+STA $4003
+JMP CLEANUP
+