[6502] Simple moving sprite.

define NULL $00
define BUFFMAX $FF
define CPOSL $DD
define CPOSH $DE
define SPRX  $A0
define SPRY  $B0

; Code

START:  LDA #00     ; Entry point
    STA SPRX
    LDA #02
    STA SPRY
DRAWL:  LDA SPRX    ; Load sprite coords
    PHA     ;
    LDA SPRY    ;
    PHA
    JSR spSTART ; Draw sprite
    JSR CLRSCR
    INC SPRX
    JMP DRAWL

spSTART:PLA      ; Setup for RTS
    TAX
    PLA
    TAY
    PLA      ; Cursor pos MSB
    STA CPOSH    ; Write MSB
    PLA      ; Cursor pos LSB
    STA CPOSL    ; Write LSB
    TYA      ; Load return address
    PHA
    TXA
    PHA
    LDA #00      ; Initalize Registers
    LDX #00
    LDY #00
spLOOP: LDA spr_arrow, X ; Load pixel
    CMP #BUFFMAX     ; Is last byte?
    BEQ spSPREND     ; Exit routine
    STA (CPOSL),Y    ; Write pixel to screen
    INX      ; Next pixel
    INY      ; Move cursor right
    CMP #NULL    ; Is last pixel in row?
    BNE spLOOP   ; Read next pixel in row
spLINE: LDA CPOSL    ; Load cursor pos LSB
    LDY #00      ; Reset cursor X
    CLC      ; AdjustAfterAddition?
    ADC #32          ; New line
    STA CPOSL    ; Write cursor pos LSB
    BCS spLINE16     ; Check if adjust
    JMP spLOOP   ; Next pixel
spLINE16: LDA CPOSH  ; Load cursor pos MSB
      INC A      ; Add one
      STA CPOSH  ; Write cursor pos MSB
      JMP spLOOP     ; Next pixel


spSPREND: RTS ; Breakpoint

CLRSCR:  LDX #00
     LDA #00
clrLOOP: STA $0200,X
     INX
     CPX #$FF
     BNE clrLOOP
     RTS

; Data
spr_arrow:
    DCB $11,$11,$11,$11,$11,$00
    DCB $11,$05,$05,$05,$05,$11,$00
    DCB $11,$05,$05,$05,$05,$05,$11,$00
    DCB $11,$05,$05,$05,$05,$05,$05,$11,$00
    DCB $11,$05,$05,$05,$05,$05,$11,$00
    DCB $11,$05,$05,$05,$05,$11,$00
    DCB $11,$11,$11,$11,$11,$00,$FF