SPO600 Lab3 - 6502 Assembly Language Math Lab

 ; zero-page variable locations define ROW $20 ; current row define COL $21 ; current column define POINTER $10 ; ptr: start of row define POINTER_H $11 ; constants define DOT $01 ; dot colour location define CURSOR $04 ; purple colour setup: lda #$0f ; set initial ROW,COL sta ROW sta COL LDA #$01 STA DOT draw: jsr draw_cursor getkey: ldx #$00 ; clear out the key buffer lda $ff ; get a keystroke stx $ff cmp #$30 bmi getkey cmp #$40 bpl continue SEC sbc #$30 tay lda color_pallete, y sta DOT jmp done continue: cmp #$43 ; handle C or c beq clear cmp #$63 beq clear cmp #$80 ; if not a cursor key, ignore bmi getkey cmp #$84 bpl getkey pha ; save A lda DOT ; set current position to DOT sta (POINTER),y jsr draw_on_quads pla ; restore A cmp #$80 ; check key == up bne check1 dec ROW ; ... if yes, decrement ROW jmp done check1: cmp #$81 ; check key == right bne check2 inc COL ; ... if yes, increment COL jmp done check2: cmp #$82 ; check if key == down bne check3 inc ROW ; ... if yes, increment ROW jmp done check3: cmp #$83 ; check if key == left bne done dec COL ; ... if yes, decrement COL clc bcc done clear: lda table_low ; clear the screen sta POINTER lda table_high sta POINTER_H ldy #$00 tya c_loop: sta (POINTER),y iny bne c_loop inc POINTER_H ldx POINTER_H cpx #$06 bne c_loop done: clc ; repeat bcc draw draw_cursor: lda ROW ; ensure ROW is in range 0:0F and #$0f sta ROW lda COL ; ensure COL is in range 0:0F and #$0f sta COL ldy ROW ; load POINTER with start-of-row lda table_low,y sta POINTER lda table_high,y sta POINTER_H ldy COL ; store CURSOR at POINTER plus COL lda #CURSOR sta (POINTER),y rts draw_on_quads: LDA POINTER ;; save the pointer to the PHA ;; original location in top_left_quad LDA POINTER_H PHA ; top right quadrant LDA #$10 CLC SBC COL CLC ADC #$10 TAY LDA DOT STA (POINTER),y TYA PHA ; save the y offset ; bottom left quadrant lda #$10 ; load POINTER with start-of-row CLC SBC ROW CLC ADC #$10 TAY lda table_low,y sta POINTER lda table_high,y sta POINTER_H ldy COL ; store CURSOR at POINTER plus COL lda DOT sta (POINTER),y PLA TAY ; bottom right quadrant lda DOT sta (POINTER),y PLA STA POINTER_H PLA STA POINTER RTS ; these two tables contain the high and low bytes ; of the addresses of the start of each row table_high: dcb $02,$02,$02,$02,$02,$02,$02,$02 dcb $03,$03,$03,$03,$03,$03,$03,$03 dcb $04,$04,$04,$04,$04,$04,$04,$04 dcb $05,$05,$05,$05,$05,$05,$05,$05, table_low: dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 dcb $00,$20,$40,$60,$80,$a0,$c0,$e0 color_pallete: dcb $01,$02,$03,$04,$05,$06,$07,$08,$09,$0a