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EdmundC

Sep 8th, 2024

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ASM (NASM) 2.19 KB | None | 0 0

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* = $0801 ; Start program at address $0801 (BASIC start)
; Standard BASIC header
.word $080b ; Next line
.word $000a ; Line number 10
.byte $9e ; BASIC token for SYS
.byte "2064",0 ; SYS 8292 to start the game
.word $0000 ; End of BASIC program
; Start of Assembly code
.org $2064 ; Start our assembly program at $2064
; Initialize the screen
START:
lda #$00 ; Set background to black
sta $d020 ; Write to border color register
sta $d021 ; Write to background color register
jsr CLEAR_SCREEN ; Clear the screen
; Initial player setup
lda #20 ; Initial player X position
sta PLAYER_X ; Store in player X position
MAIN_LOOP:
jsr DRAW_PLAYER ; Draw the player plane
; Get joystick input for left/right movement
lda $dc00 ; Read joystick
and #%00000001 ; Check for left (bit 0)
beq MOVE_LEFT
lda $dc00
and #%00000010 ; Check for right (bit 1)
beq MOVE_RIGHT
jmp MAIN_LOOP
MOVE_LEFT:
lda PLAYER_X
cmp #1 ; Don't move off screen to the left
beq MAIN_LOOP
dec PLAYER_X ; Move player left
jmp MAIN_LOOP
MOVE_RIGHT:
lda PLAYER_X
cmp #39 ; Don't move off screen to the right (40 columns)
beq MAIN_LOOP
inc PLAYER_X ; Move player right
jmp MAIN_LOOP
DRAW_PLAYER:
lda PLAYER_X
sta TEMP ; Store X position in TEMP
lda #$20 ; ASCII code for space (clear the old position)
sta $0400 + 23*40 + TEMP ; Clear old position at row 23
lda PLAYER_X ; Reload player X
lda #$41 ; ASCII code for 'A' (player airplane)
sta $0400 + 23*40 + PLAYER_X ; Draw player airplane
rts
CLEAR_SCREEN:
ldx #0
CLEAR_LOOP:
lda #$20 ; Fill screen with spaces
sta $0400,x
sta $0428,x
sta $0450,x
sta $0478,x
sta $04a0,x
sta $04c8,x
sta $04f0,x
sta $0518,x
inx
bne CLEAR_LOOP ; Loop until all screen is cleared
rts
; Variables
PLAYER_X:
.byte 0 ; Player X position (column)
TEMP:
.byte 0 ; Temporary storage

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