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 |
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ChibiAkumas Tutorials
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Lesson P9 - Bitmap Functions on the C64 |
Text Graphics
The characters shown onscreen are selected by the bytes in the memory range $0400-$07FF, 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 |
| 0 | Text Screen Mem - Low nibble | $0400-$07FF ----CCCC |
| 1 | Text Screen Mem - High nibble | $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 |
| 00 | Background Color | $D021 |
| 01 | Text Screen Mem - Low nibble | $0400-$07FF ----CCCC |
| 10 | Text Screen Mem - High nibble | $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 |
| $D016 | Screen control register #2 | ---MWHHH | M=Multicolor W=scr width H=horiz scroll |
| $D018 | Memory setup register. | SSSSTTT- | T=Text/Bmp screen address S=Screen (color) address |
| $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 |
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!
Sprites are 21 vertical lines and 63 bytes each...
In 1bpp (2 color) mode this makes sprites 24x63...
In 2bpp (4 color) mode they are 12x63...
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.
| Address | Purpose | Bits | Meaning |
| $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 |
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 / Sawtooth / Triangle / - test / Ring mod / Sync /Gate |
| $D405 | Voice #1 Attack and Decay length | AAAADDDD | Atack / Decay |
| $D406 | Voice #1 Sustain volume and Release length. | SSSSRRRR | Sustain / Release |
| $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 / Sawtooth / Triangle / - test / Ring mod / Sync /Gate |
| $D40C | Voice #2 Attack and Decay length | AAAADDDD | Atack / Decay |
| $D40D | Voice #2 Sustain volume and Release length. | SSSSRRRR | Sustain / Release |
| $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 / Sawtooth / Triangle / - test / Ring mod / Sync /Gate |
| $D413 | Voice #3 Attack and Decay length. | AAAADDDD | Atack / Decay |
| $D414 | Voice #3 Sustain volume and Release length. | SSSSRRRR | Sustain / Release |
| $D415 | Filter cut off frequency L | -----LLL | |
| $D416 | Filter cut off frequency H | HHHHHHHH | |
| $D417 | Filter control | RRRREVVV | R=Resonance / 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 |
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