udemy_atari2600/rainbow.dasm at main · DMinsky/udemy_atari2600 · GitHub

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	processor 6502
	include "vcs.h"
	include "macro.h"

	seg code
	org $f000

Start:
	CLEAN_START	; Usual start routine defined in macro.h

; Start a new fram by turnin on VBLANK and VSYNC
NextFrame:
	lda #2
	sta VBLANK
	sta VSYNC

; Generate three lines for VSYNC
	sta WSYNC
	sta WSYNC
	sta WSYNC
	lda #0
	sta VSYNC

; Generate 37 lines for the VBLANC
	ldx #37
VBlankLoop:
	sta WSYNC
	dex
	bne VBlankLoop
	sta VBLANK

; Draw 192 visible scanlines
	ldx #192
VisibleLoop:
	stx COLUBK	; Changing background color with every line
	sta WSYNC
	dex
	bne VisibleLoop

; Generate Overscan lines
	lda #2
	sta VBLANK
	ldx #30

OverscanLoop:
	sta WSYNC
	dex
	bne OverscanLoop
	sta VBLANK

	jmp NextFrame

	org $fffc
	.word Start
	.word Start