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|
; vcsdrive - Simple Atari VCS driving game
;
; Copyright (C) 2024 Ian Cowburn (ianc@noddybox.demon.co.uk)
;
; This program is free software: you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, either version 3 of the License, or
; (at your option) any later version.
;
; This program is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with this program. If not, see <http://www.gnu.org/licenses/>.
;
; -------------------------------------------------------------------------
;
; Code
;
processor 6502
option output-file,vcsdrive.bin
include vcs.asm
bgcolour equ $81
org $f000
; Set up stack pointer
start:
sei
cld
ldx #$ff
txs
; Initialise page zero
lda #0
.zero:
sta $0,x
dex
bne zero
; Start frame
next_frame:
lda #2
ldy bgcolour
sta VBLANK
sty COLUBK
iny
sta VSYNC
sty COLUBK
iny
sta WSYNC
sty COLUBK
iny
sta WSYNC
sty COLUBK
iny
sta WSYNC
sty COLUBK
iny
lda #0
sta VSYNC
; Do VBLANK
ldx #37
.vblank:
sta WSYNC
dex
bne vblank
lda #0
sta VBLANK
; Draw 192 visible scan lines
ldx #192
.scanlines:
sty COLUBK
sta WSYNC
iny
dex
bne scanlines
; Complete the frame
lda #2
sta VBLANK
ldx #30
.complete:
sty COLUBK
iny
sta WSYNC
dex
bne complete
dec bgcolour
jmp next_frame
; Set start adresses and pad ROM
org $fffc
word start
word start
|
