2x4 Scroll

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;0PG $A3-$A6
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SCROLL   LDA $A5
         CLC
SC9      SBC #$02
         CMP #$C0
         BCS SC7
         ADC #$08
         STA $A5
         LDX #$00
SC1      LDA $0749,X
         STA $0748,X
         LDA $0771,X
         STA $0770,X
         LDA $0799,X
         STA $0798,X
         LDA $07C1,X
         STA $07C0,X
         INX
         CPX #$27
         BNE SC1
         DEC $A6
         BEQ SC2
         LDA $076E
         CLC
         ADC #$20
SCX      STA $076F
         CLC
         ADC #$40
         STA $0797
         CLC
         ADC #$40
         STA $07BF
         CLC
         ADC #$40
         STA $07E7
         RTS
SC2      LDY #$00
         LDA #$02
         STA $A6
         LDA ($A3),Y
         BNE SC3
SC8      LDX #$00
         LDY #$09
         STX $A3
         STY $A4
         RTS
SC0      LDA #$C8
         STA $A5
         LDA #$01
         STA $A6
         BNE SC8
SC3      CMP SCD,Y
         BEQ SC4
         INY
         CPY #$07
         BNE SC3
         JSR SCX
SC6      INC $A3
         BNE SC5
         INC $A4
SC5      RTS
SC4      STY SC9+1
         JMP SC6
SC7      STA $A5
         RTS
SCD      .BYTE $80,$81,$82,$83,$84,$85
         .BYTE $86
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