6510 Assembly programming for the Commodore 64

The C64 is one of the most popular computers of all time, although limited to just 64k, it rivalled its competitors with hardware sprites and scrolling,

its 6510 CPU is a 6502 with built in IO ports... the is no programming difference

	C64	C128
Cpu	1mhz 6510 (6502 base)	2mhz 8502
Ram	64k	128k
Sprites	8 per line (24x21 px)	8 per line (24x21 px)
Resolution	320x200 / 160x200	320x200 / 160x200
Colors	4 per 8x8 tile from 16	4 per 8x8 tile from 16
Sound chip	SID	SID

ChibiAkumas Tutorials

	Lesson H2 - Hello World on the C64
	Lesson S2 - Bitmap Drawing on the C64
	Lesson P9 - Bitmap Functions on the C64
	Lesson P30 - Sound on the C64
	Lesson P36 - Hardware Sprites on the C64

*** Linux and Mac users! ***

Viewer "Kevin Thomas" has done a lot of work porting the C64 Chibiakumas tutorials to Linux and Unix - so if you're using those systems, you should probably check out his work over Here!

Text Graphics

The characters shown onscreen are selected by the bytes in the memory range $0400-$07FF (These addresses change as the screenbase moves), the colors of the tiles are selected per 8x8 square, from the registers at $D800-$DBE7... only the Low nibble of this area is used.

Bitmap Graphics
There are two modes for Bitmap graphics on the C64

Normal mode is 320x200... it has 2 colors per 8x8 tile, the "Bitmap data" is typically located between $2000-$3FFF, this is a 1 bpp bitmap, each tile will get its background color from the low nibble of $D020, and it:s foreground color from the low nibble of $D800-$DBE7

Bits	Detail	Address	Bits
0	Text Screen Mem - Low nibble	ScreenBase+$0400-$07FF	----CCCC
1	Text Screen Mem - High nibble	ScreenBase+$0400-$07FF	CCCC----

Multicolor Mode is 160x200 , it has 4 colors per 4x8 tile, but setting those colors is more tricky... again it uses a bitmap screen at $2000-$3FFF, but is 2bpp... it uses a 160x200, 2 bits for each pixel choose a color from 1 of 4 locations

Bits	Detail	Address	Bits
00	Background Color	$D021	----CCCC
01	Text Screen Mem - Low nibble	ScreenBase+$0400-$07FF	----CCCC
10	Text Screen Mem - High nibble	ScreenBase+$0400-$07FF	CCCC----
11	Color Memory - Low Nibble	$D800-$DBFF	----CCCC

The Border Color is defined by $D020

Graphics Memory and ports

Address	Description	Bits	Meaning
$0400-$07E7	Default area of screen memory		(1000 bytes).
$2000-$3FFF	BMP Screen Ram
$D000-$D7FF	Char ROM in uppercase/graphics character set		(2048 bytes, 256 entries)
$D800-$DFFF	Char ROM in lowercase/uppercase character set		(2048 bytes, 256 entries)
$D011	Screen control register #1.	LXMSHVVV	L=Cur Line X=extended BG M=mode (Txt/Bmp)S=screen on H=height V=Vert scroll
$D012	Raster line of IRQ (RW)	LLLLLLLL	L=Raster Line of IRQ
$D016	Screen control register #2	---MWHHH	M=Multicolor W=scr width H=horiz scroll
$D018	Memory setup register.	SSSSTtt-	Ttt=Text screen addr offset (multiples of $800) T=Bmp screen addr offet ($0000/$2000) S=Screen (color) addr offset (multiples of $400)
$D020	Border color	----CCCC	C=color
$D021	Background color	----CCCC	C=color
$D022	Extra background color #1	----CCCC	C=color
$D023	Extra background color #2	----CCCC	C=color
$D024	Extra background color #3	----CCCC	C=color
$D800-$DBE7	Color RAM	----CCCC	C=color (1000 bytes).

Palette

0	1	2	3	4	5	6	7
8	9	A	B	C	D	E	F

C64 Sprites

The Sprite pointers for the bitmap data are a single byte... multiplying the sprite pointer by 64 will give the address of the sprite *within the 16k bank of Vram* (so must be in the range $0000-$3FFF)...
$1000-$2000 and $9000-$A000 are seen by the VIC as character ROM, so sprites cannot be in this area!
We can move our screen base to something more convenient... so for example with a screen base of $4000 (Screen ram at $6000)- our sprites can be at $5000

$D018 Memory setup register.	$DD00 Vic 2 bank (Bottom 2 bits)	Screen Base	Sprite Patterns	Sprite Pointers
%00011000 (Screen base $2000 / Colors at $400)	%------10 (Bank $4000-7FFF)	$6000 ($4000+$2000)	$5000 (one option) $4000+?	$47F8 ($4000+$7F8)

Sprites are 21 vertical lines and 63 bytes each. With one unused byte this makes a 64 byte pattern size.
In 1bpp (2 color) mode this makes sprites 24x21.
In 2bpp (4 color) mode they are 12x21.

In both modes, Color 0 is Transparent
In 2bpp mode color 1,2 are read from $D025/6 and color 3 is the sprite color.

The Top Left first visible co-ordinate is (24,50)

Address	Purpose	Bits	Meaning
ScreenBase+ $07F8-$07FF	Sprite pointers (default - will change if screen moved)	SSSSSSSS	s*64=memory address
$D000	Sprite #0 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D001	Sprite #0 Y-coordinate	YYYYYYYY
$D002	Sprite #1 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D003	Sprite #1 Y-coordinate	YYYYYYYY
$D004	Sprite #2 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D005	Sprite #2 Y-coordinate	YYYYYYYY
$D006	Sprite #3 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D007	Sprite #3 Y-coordinate	YYYYYYYY
$D008	Sprite #4 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D009	Sprite #4 Y-coordinate	YYYYYYYY
$D00A	Sprite #5 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D00B	Sprite #5 Y-coordinate	YYYYYYYY
$D00C	Sprite #6 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D00D	Sprite #6 Y-coordinate	YYYYYYYY
$D00E	Sprite #7 X-coordinate	XXXXXXXX	(only bits #0-#7).
$D00F	Sprite #7 Y-coordinate	YYYYYYYY
$D010	Sprite #0-#7 X-coordinates	76543210	(bit #8)
$D015	Sprite enable register	76543210	1=on
$D017	Sprite double height register	76543210
$D01B	Sprite priority register	76543210
$D01C	Sprite multicolor mode register	76543210	0=2 color 1=4color
$D01D	Sprite double width register	76543210
$D01E	Sprite-sprite collision register	76543210
$D01F	Sprite-background collision reg	76543210
$D025	Sprite extra color #1	----CCCC
$D026	Sprite extra color #2	----CCCC
$D027	Sprite #0 color	----CCCC
$D028	Sprite #1 color	----CCCC
$D029	Sprite #2 color	----CCCC
$D02A	Sprite #3 color	----CCCC
$D02B	Sprite #4 color	----CCCC
$D02C	Sprite #5 color	----CCCC
$D02D	Sprite #6 color	----CCCC
$D02E	Sprite #7 color	----CCCC

Interrupt Vectors

The standard 6502 interrupt vectors from $FFFA+ are ROM, however these jump to vectors in low memory addresses. IRQ and BRK interrupts push A,X and Y onto the stack in that order.

From	To	Function	Registers Pushed
$0314	$0315	IRQ	A X Y
$0316	$0317	BRK	A X Y
$0318	$0319	NMI

SID sound chip
The SID chip uses memory addresses $D400-$D41C

Address	Description	Bits	Meaning
$D400	Voice #1 frequency L	LLLLLLLL
$D401	Voice #1 frequency H	HHHHHHHH	Higher values=higher pitch
$D402	Voice #1 pulse width L	LLLLLLLL
$D403	Voice #1 pulse width H	----HHHH
$D404	Voice #1 control register	NPST-RSG	Noise / Pulse / Saw-tooth / Triangle / - test / Ring mod / Sync /Gate
$D405	Voice #1 Attack and Decay length	AAAADDDD	Attack / Decay (0=fastest)
$D406	Voice #1 Sustain volume and Release length.	VVVVRRRR	Sustain Volume / Release (0=fastest)
$D407	Voice #2 frequency L	LLLLLLLL
$D408	Voice #2 frequency H	HHHHHHHH	Higher values=higher pitch
$D409	Voice #2 pulse width L	LLLLLLLL
$D40A	Voice #2 pulse width H	----HHHH
$D40B	Voice #2 control register	NPST-RSG	Noise / Pulse / Saw-tooth / Triangle / - test / Ring mod / Sync /Gate
$D40C	Voice #2 Attack and Decay length	AAAADDDD	Attack / Decay (0=fastest)
$D40D	Voice #2 Sustain volume and Release length.	VVVVRRRR	Sustain Volume / Release rate (0=fastest)
$D40E	Voice #3 frequency L	LLLLLLLL
$D40F	Voice #3 frequency H	HHHHHHHH	Higher values=higher pitch
$D410	Voice #3 pulse width L	LLLLLLLL
$D411	Voice #3 pulse width H	----HHHH
$D412	Voice #3 control register.	NPST-RSG	Noise / Pulse / Saw-tooth / Triangle / - test / Ring mod / Sync /Gate
$D413	Voice #3 Attack and Decay length.	AAAADDDD	Attack / Decay (0=fastest)
$D414	Voice #3 Sustain volume and Release length.	VVVVRRRR	Sustain Volume / Release (0=fastest)
$D415	Filter cut off frequency L	-----LLL	Cut off frequency
$D416	Filter cut off frequency H	HHHHHHHH	Cut off frequency
$D417	Filter control	RRRREVVV	R=Resonance (0=off) / External / V= Voice 3-1
$D418	Volume and filter modes	MHBLVVVV	Mute3 / Highpass / Bandpass / Lowpass / Volume (0=silent)
$D41B	Voice #3 waveform output. (Read only)	DDDDDDDD
$D41C	Voice #3 ADSR output. (Read only)	DDDDDDDD

C64 Mouse (1351)

The C64 mouse has 2 modes, The first makes it work as a plain joystick), the second gives analog movements, which are passed via the X,Y paddle, with the fire buttons passed through the Joystick digital buttons

See the official manual for more details of the mouse

Address	Description	Normal Bits	Mouse Bits	Meaning
$D419	Paddle X value (Mouse X move)	xxxxxxxx	xPPPPPPn	x=dont care (ignored) / P=Mouse Pos MOD 64 / n=noise bit
$D41A	Paddle Y value (Mouse Y move)	yyyyyyyy	xPPPPPPn	x=dont care (ignored) / P=Mouse Pos MOD 64 / n=noise bit
$DC01	CIA1: Port B, keyboard matrix rows and joystick #1	---FRLDU	---L---R	Left / Right Mousebuttons

CIAs

Address	Description	Bits	Meaning
$DC00	CIA1: Port A, keyboard matrix columns and joystick #2
$DC01	CIA1: Port B, keyboard matrix rows and joystick #1
$DC02	CIA1: Port A data direction register.
$DC03	CIA1: Port B data direction register.
$DC04-$DC05	CIA1: Timer A. RW
$DC06-$DC07	CIA1: Timer B. RW
$DC08	CIA1: Time of Day, tenth seconds (in BCD). Values: $00-$09. RW
$DC09	CIA1: Time of Day, seconds (in BCD). Values: $00-$59. RW
$DC0A	CIA1: Time of Day, minutes (in BCD). Values: $00-$59. RW
$DC0B	CIA1: Time of Day, hours (in BCD). RW
$DC0C	CIA1: Serial shift register. (Bits are read and written upon every positive edge of the CNT pin.)
$DC0D	CIA1: Interrupt control and status register. RW	F--fSTBA	F=fill all / Interrupt occurred / f=Flag pine / S=Shift register complete byte recieved / T=alarm Time / B=TimerB / A= TimerA
$DC0E	CIA1: Timer A control register.
$DC0F	CIA1: Timer B control register.
$DC10-$DCFF	CIA1: Register Mirror (repeated every $10, 16 bytes)
$DD00	CIA2: Port A, serial bus access.	DCdcATBB	Serial Bus: D=Data in C=Clock In / d=data out c=clock out A=ATN Out T=TXD Out (RS232) BB=Vic2 banks (Screen VRAM base)
$DD01	CIA2: Port B, RS232 access.
$DD02	CIA2: Port A data direction register
$DD03	CIA2: Port B data direction register
$DD04-$DD05	CIA2: Timer A
$DD06-$DD07	CIA2: Timer B
$DD08	CIA2: Time of Day, tenth seconds (in BCD). Values: $00-$09.
$DD09	CIA2: Time of Day, seconds (in BCD). Values: $00-$59.
$DD0A	CIA2: Time of Day, minutes (in BCD). Values: $00-$59.
$DD0B	CIA2: Time of Day, hours (in BCD)
$DD0C	CIA2: Serial shift register. (Bits are read and written upon every positive edge of the CNT pin.)
$DD0D	CIA2: Interrupt control and status register.	F--fSTBA	F=fill all / Interrupt occurred / f=Flag pine / S=Shift register complete byte recieved / T=alarm Time / B=TimerB / A= TimerA
$DD0E	CIA2: Timer A control register.
$DD0F	CIA2: Timer B control register
$DD10-$DDFF	CIA2: Register mirror (repeated every $10, 16 bytes).