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).