Inside the VIC-II

Overview

The MOS Technology VIC-II (6567 NTSC / 6569 PAL) is the Commodore 64's video chip. It paints the 40×25 character screen, drives eight hardware sprites, scrolls backgrounds smoothly in hardware, and exposes 47 registers that let programmers control every aspect of the display. Its quirks — especially badlines — defined the timing tricks that demo coders exploited for decades.

Fast facts

Display modes: 320×200 hi-res (two colours per cell) or 160×200 multicolour (four colours per cell), plus bitmap and extended-colour variants.
Palette: 16 fixed colours with famously rich blues and browns.
Sprites: eight 24×21 pixel sprites, independently positioned, with 2× horizontal stretch ($D01D) and 2× vertical stretch ($D017).
Registers: 47 at $D000-$D02E (53248-53294 decimal).
Timing: steals CPU cycles on certain scanlines, so code must dance around the raster beam.

Chip variants

6567 (NTSC) — ~60Hz, 263 raster lines per frame, 65 CPU cycles per line
6569 (PAL) — ~50Hz, 312 raster lines per frame, 63 CPU cycles per line

Most programming is identical between variants. Timing-critical code (raster interrupts, sprite multiplexing, music players) needs region-specific values.

Register map

The VIC-II's registers live at $D000-$D02E (53248-53294 decimal). Writing to these addresses controls display hardware directly.

Address	Register	Purpose
$D000-$D001	MOB0X, MOB0Y	Sprite 0 position
$D002-$D003	MOB1X, MOB1Y	Sprite 1 position
$D004-$D005	MOB2X, MOB2Y	Sprite 2 position
$D006-$D007	MOB3X, MOB3Y	Sprite 3 position
$D008-$D009	MOB4X, MOB4Y	Sprite 4 position
$D00A-$D00B	MOB5X, MOB5Y	Sprite 5 position
$D00C-$D00D	MOB6X, MOB6Y	Sprite 6 position
$D00E-$D00F	MOB7X, MOB7Y	Sprite 7 position
$D010	MSIGX	High X bits (for X > 255)
$D011	SCROLY	Vertical scroll, screen enable, bitmap mode, raster high bit
$D012	RASTER	Current raster line counter
$D013-$D014	LPENX, LPENY	Light pen position
$D015	SPENA	Sprite enable bits
$D016	SCROLX	Horizontal scroll, multicolour mode
$D017	YXPAND	Sprite Y expansion (double height)
$D018	VMCSB	Memory pointers for screen and character set
$D019	VICIRQ	Interrupt status
$D01A	IRQMASK	Interrupt enable
$D01B	SPBGPR	Sprite-background priority
$D01C	SPMC	Sprite multicolour enable
$D01D	XXPAND	Sprite X expansion (double width)
$D01E	SPSPCL	Sprite-sprite collision
$D01F	SPBGCL	Sprite-background collision
$D020	EXTCOL	Border colour
$D021	BGCOL0	Background colour 0
$D022	BGCOL1	Background colour 1
$D023	BGCOL2	Background colour 2
$D024	BGCOL3	Background colour 3
$D025	SPMC0	Sprite multicolour 0
$D026	SPMC1	Sprite multicolour 1
$D027-$D02E	SP0COL-SP7COL	Individual sprite colours

Border and background colours

The simplest VIC-II registers to use:

POKE 53280,0  : REM Border colour (black)
POKE 53281,1  : REM Background colour (white)

Colour values (0-15):

0=Black   1=White    2=Red      3=Cyan
4=Purple  5=Green    6=Blue     7=Yellow
8=Orange  9=Brown   10=Lt Red  11=Dk Grey
12=Grey  13=Lt Grn  14=Lt Blue 15=Lt Grey

Games use border colour for visual effects — flash red on damage, pulse with music, change per level.

Screen RAM configuration ($D018)

Default value: $14 (20 decimal)

Screen RAM at $0400 (1024)
Character ROM at $1000

Bit layout:

Bits 7-4: Screen RAM location (×$0400)
Bits 3-1: Character set location (×$0800)
Bit 0:    Unused

Example — move screen to $0C00:

POKE 53272,(PEEK(53272) AND 15) OR 48

Calculation: $0C00 / $0400 = 3, so bits 7-4 = 3 (0011), shifted left 4 bits = 48.

Games use this for double-buffering (draw to hidden screen, flip display).

Display control ($D011)

Bit layout:

Bit 7:    Raster compare bit 8 (for $D012)
Bit 6:    Extended colour mode
Bit 5:    Bitmap mode
Bit 4:    Screen enable (0=blank screen)
Bit 3:    25/24 row select (1=25 rows)
Bits 2-0: Vertical scroll (0-7 pixels)

Default value: $1B (27 decimal) — 25 rows, screen on, text mode, scroll=3.

Example — enable bitmap mode:

POKE 53265,PEEK(53265) OR 32

Bit 5 set = bitmap mode. Screen now displays 320×200 bitmap instead of 40×25 text.

Horizontal control ($D016)

Bit layout:

Bit 5:    Reset bit (always 0)
Bit 4:    Multicolour mode
Bit 3:    40/38 column select (1=40 columns)
Bits 2-0: Horizontal scroll (0-7 pixels)

Default value: $08 (8 decimal) — 40 columns, single colour, scroll=0.

Example — enable multicolour text:

POKE 53270,PEEK(53270) OR 16

Multicolour mode gives 4 colours per character cell but halves horizontal resolution (160×200 effectively).

Raster register ($D012)

Read this register to:

Time code to specific screen positions
Create raster interrupts (change colours mid-screen)
Synchronise sprite movement
Split screen effects (status bars, parallax)

Example — wait for raster line 100:

10 IF PEEK(53266)<>100 THEN 10
20 POKE 53280,2  : REM Change border when line 100 reached

Sprite enable ($D015)

Example — enable sprites 0, 1, and 2:

POKE 53269,7  : REM Binary 00000111 = sprites 0-2 on

Turn off sprite 1:

POKE 53269,PEEK(53269) AND 253  : REM Clear bit 1

Sprite positions ($D000-$D010)

Each sprite has X and Y registers. Y is 8-bit (0-255), X is 9-bit (0-511) using $D010 for high bits.

Example — position sprite 0 at (150, 100):

POKE 53248,150  : REM X low byte
POKE 53249,100  : REM Y position
POKE 53264,PEEK(53264) AND 254  : REM Clear X high bit

For X > 255:

POKE 53248,260 AND 255  : REM Low byte (260-256=4)
POKE 53264,PEEK(53264) OR 1  : REM Set bit 0 in $D010

Sprite data

Sprite shapes are stored in 64-byte blocks (63 bytes used, last byte unused). Each sprite is 24×21 pixels, stored as 3 bytes per row × 21 rows.

Sprite pointers: Screen RAM + $03F8-$03FF (1016-1023)

Pointer for sprite 0 at 2040
Pointer for sprite 1 at 2041
...
Pointer for sprite 7 at 2047

Example — set sprite 0 to block 13:

POKE 2040,13  : REM Sprite data at 13*64 = 832

Create simple sprite (vertical line):

10 FOR I=832 TO 894
20 POKE I,255  : REM First byte of each row = 11111111
30 NEXT I
40 POKE 2040,13  : REM Point sprite 0 to block 13
50 POKE 53269,1  : REM Enable sprite 0
60 POKE 53248,150  : REM X position
70 POKE 53249,100  : REM Y position

Collision detection

Sprite-sprite: $D01E (53278)
Sprite-background: $D01F (53279)

Both registers use bit flags (bit 0 = sprite 0, etc.).

Example — check if sprite 0 hit anything:

10 C=PEEK(53278)  : REM Sprite-sprite
20 IF C AND 1 THEN PRINT "SPRITE 0 HIT ANOTHER SPRITE"
30 B=PEEK(53279)  : REM Sprite-background
40 IF B AND 1 THEN PRINT "SPRITE 0 HIT BACKGROUND"

Important: Reading these registers clears them. Check once per frame.

Display modes

The VIC-II supports multiple display modes via $D011 and $D016:

Mode	$D011 bit 5-6	$D016 bit 4	Resolution	Colours
Text	00	0	40×25 chars	2 per char
Multicolour text	00	1	40×25 chars	4 per char
Bitmap	01	0	320×200 pixels	2 per 8×8
Multicolour bitmap	01	1	160×200 pixels	4 per 4×8
Extended colour	10	0	40×25 chars	4 backgrounds

Most games use bitmap modes for graphics, text mode for UI.

Badlines

Every 8th raster line in the visible area, the VIC-II "steals" 40 CPU cycles to fetch screen data. These are badlines — they run from raster line 48 to 247, occurring whenever the bottom three bits of $D012 match the bottom three bits of $D011 (the YSCROLL register). With the default YSCROLL value of 3, badlines fall on lines 51, 59, 67…251.

Effect: CPU halts for 40 cycles. Code timing becomes unpredictable.

Solutions:

Execute time-critical code outside badlines
Disable screen during tight loops (POKE 53265,PEEK(53265) AND 239)
Use raster interrupts to run code in overscan area

Demo coders exploit badlines for FLI (Flexible Line Interpretation): by writing YSCROLL into $D011 to match the current raster line's low three bits, every line becomes a badline. Then changing $D018 each line points the VIC-II at a fresh character set per row, yielding 8 colours per 8×8 cell instead of 2.

Famous quirks

Sprite priority: sprites can pass in front of or behind the background with per-sprite control bits.
Open borders: the top/bottom border opens via $D011 bit 3 (switch to 24-row mode at the right cycle); the side borders open via $D016 bit 3 (switch to 38-column mode). Both rely on cycle-exact timing relative to the raster beam.
Sprite crunching: repositioning sprites mid-frame creates the illusion of more than eight on screen — critical for shooters.

Practical example: colour cycling border

10 FOR C=0 TO 15
20 POKE 53280,C
30 FOR D=1 TO 50:NEXT D
40 NEXT C
50 GOTO 10

Cycles border through all 16 colours with delay.

Practical example: raster bars

10 POKE 53265,PEEK(53265) AND 239  : REM Blank screen
20 FOR R=0 TO 255
30 IF PEEK(53266)<>R THEN 30
40 POKE 53280,(R AND 15)
50 NEXT R
60 GOTO 20

Creates animated colour bars by changing border colour every raster line.

Historical notes

The VIC-II was designed by Al Charpentier at MOS Technology in 1981, evolving from the VIC chip in the VIC-20. Charpentier added hardware sprites (building on the player-missile graphics ideas from earlier Atari hardware), smooth scrolling registers, and collision detection — features that made arcade-quality games possible on a $595 home computer, undercutting competitors dramatically.

Early games used the VIC-II's built-in features straightforwardly — sprites for player/enemies, text mode for screens. By 1985, programmers discovered register tricks: open borders (full-screen graphics), sprite multiplexing (reusing sprites mid-frame), and FLI modes (changing graphics mode per scanline). Demo groups like Crest and Censor Design pushed furthest, creating effects Commodore's engineers never imagined — and still find new raster tricks four decades later.

The graphics chip that defined the Commodore 64

Overview

Fast facts

Chip variants

Register map

Border and background colours

Screen RAM configuration ($D018)

Display control ($D011)

Horizontal control ($D016)

Raster register ($D012)

Sprite enable ($D015)

Sprite positions ($D000-$D010)

Sprite data

Collision detection

Display modes

Badlines

Famous quirks

Practical example: colour cycling border

Practical example: raster bars

Historical notes

See also