View difference between Paste ID: <a href="/P8sbrLud">P8sbrLud</a> and <a href="/aCwE7795">aCwE7795</a>

; // Summary
1		; // Summary
2		; // A Very Basic NES ROM that displays 1 color: Blue
3
4		.segment "INESHDR"
5		.byt "NES",$1A
6		.byt 1 ; 1 x 16kB PRG block.
7		.byt 1 ; 1 x 8kB CHR block.
8
9		.segment "VECTORS"
10		.addr nmi, reset, irq
11
12		.segment "ZEROPAGE"
13		retraces: .res 1
14
15		; Variables
16		.segment "BSS"
17		xframes: .res 1
18		buttons: .res 1 ; Reserve 1 byte for storing the data read from controller.
19
20
21		.segment "CODE"
22		; Procedures
23		; -----------------------------------------------------------------------------
24
25		.proc reset
26		; Disable Interrupts
27		SEI
28
29		; Basic Initialization
30		LDX #0
31		STX $2000 ; General init state; NMIs (bit 7) disabled.
32		STX $2001 ; Disable rendering, i.e. turn off background & sprites.
33
34		; PPU Warmup (29658 Cycles)
35		BIT $2002 ; Clear the VPL Flag if it was set at reset time.
36		vwait1:
37		BIT $2002 ; 27384 Cycles has passed.
38		BPL vwait1
39		vwait2:
40		BIT $2002 ; 57165 Cycles has passed.
41		BPL vwait2
42
43		; Clear lingering interrupts since before reset.
44		; BIT $2002 ; Ack VBLANK NMI (if one was left over after reset); bit 7.
45
46		LDA #%00100000 ; Intensify reds
47		STA $2001
48
49		LDA #%10000000
50		STA $2000
51
52
53
54		waitfora:
55		; call subroutine to read current button state
56		JSR readjoy
57
58		; check if bit 7 of buttons is set
59		LDA #$80
60		BIT buttons
61
62	-	BNE waitfora
62	+
63		BEQ waitfora
64
65		LDA #%01000000 ; Intensify greens
66		STA $2001
67
68		LDA #%10000000
69		STA $2000
70
71		LDX #30
72		JSR waitxframes
73
74		LDA #%10000000 ; Intensify blues
75		STA $2001
76
77		LDA #%10000000
78		STA $2000
79
80		LDX #30
81		JSR waitxframes
82
83		forever:
84		JMP forever ; Infinite loop
85		.endproc
86
87		.proc readjoy
88		LDA #$01
89		STA $4016
90		STA buttons ; We use our variable!
91		LSR A
92		STA $4016
93
94		loop:
95		LDA $4016
96		LSR A ; Bit 0 -> Carry
97		ROL buttons ; Carry -> Bit 0; Bit 7 -> Carry
98		BCC loop ; Branch if Carry Clear
99		RTS
100		.endproc
101
102		.proc nmi
103		INC xframes
104		RTI
105		.endproc
106
107		.proc irq
108		RTI
109		.endproc
110
111		.proc waitxframes
112		wait: ; Wait for a frame
113		LDA xframes
114		waitonce:
115		CMP xframes
116		BEQ waitonce
117		DEX ; X = X - 1
118		BNE wait ; if X is not zero, keep going...
119		RTS
120		.endproc