Atari 2600 programming

[Harry Dodgson]

;	Billboard Demo
;	displays sonething close to, but not quite like
;	the colored billboard used in "Close Encounters..."
;	just a small demo to see what could be done
;
Start	LDX	#$FF
	TXS
	JSR	Sub0
	LDA	#$06
	STA	$09
	LDA	#$02
	STA	$0A
	LDA	#$35
	STA	$B1
	STA	$B4
	LDA	$1B
	STA	$B2
	STA	$B3
	LDA	#$00
	STA	$B6
	LDA	#$AA
	STA	$B5
Main	JSR	Sub1
	LDA	#$50
	STA	$06
	LDA	#$80
	STA	$07
	LDA	#$08
	STA	$19
	JSR	Sub2
	LDA	$0282
	AND	#$02
	BEQ	Start
	JSR	Sub3
	LDX	#$10
Loop1	NOP
	STY	$02
	DEX
	BNE	Loop1
	LDY	#$06
	LDX	#$04
Loop2	STY	#$02
	LDA	$B1
	STA	$0D
	LDA	$B2
	STA	$0E
	LDA	$B3
	STA	$0F
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	NOP
	LDA	$B4
	STA	$0D
	LDA	$B5
	STA	$0E
	LDA	$B6
	STA	$0F
	DEX
	BNE	Loop2
	LDA	#$06
	STA	$06
	STA	$07
	LDX	#$A6
Loop3	NOP
	STY	$02
	DEX
	BNE	Loop3
	JMP	Main
Sub0	CLD
	SEI
	LDX	#$00
	STX	$0281
	STX	$0283
	LDY	#$04
Loc0	STX	$00,Y
	INY
	CPY	#$20
	BNE	Loc0
	STX	$2B
	RTS
Sub1	LDY	#$FF
	STY	$02
	STY	$01
	STY	$00
	LDA	#$2A
	STA	$0295
	LDA	$0282
	AND	#$01
	BNE	Loc1
	BRK
Loc1	RTS
Sub2	LDY	$0284
	BNE	Sub2
	STY	$02
	STY	$00
	LDA	#$19
	STA	$0296
	RTS
Sub3	LDY	$0284
	BNE	Sub3
	STY	$02
	STY	$01
	STY	$2A
	RTS
	.END

-- 
Harry Dodgson Jr.               Internet:  dodgson at cs.wmich.edu
Western Michigan University
Computer Science Department        Voice:     (616) 387-5803
Kalamazoo, MI  49008