| name | c64-graphics |
| description | C64 screen graphics from the programmer's view: the five VIC-II display modes (standard/multicolor text, ECM, standard/multicolor bitmap), custom 8x8 character sets, screen/color/character memory layout, video bank selection, and smooth scrolling. Use this skill WHEN you see "how do I define custom characters", "turn on multicolor mode", "POKE 53272 / 53265 / 53270 / 53281", "$D011 $D016 $D018 bitmap mode", "switch VIC-II video banks", "where is screen RAM / color RAM", "set the bitmap base", or "smooth scroll the screen". Pairs with c64-sprites, c64-vic-ii (raster timing, full chip spec), and c64-memory-map. |
C64 Graphics (VIC-II display modes)
Programming the C64 screen: text and bitmap modes, custom charsets, the
screen/color/char memory map, video banks, and smooth scrolling. Hardware
sprites (MOBs) are the separate c64-sprites skill. For cycle-exact raster
timing, bad lines, the invalid modes, and the full register spec, use
c64-vic-ii; for ROM/RAM/IO banking under the VIC see c64-memory-map.
The VIC-II (6567 NTSC / 6569 PAL) lives at $D000–$D02E (53248–53294). A
display is 40 columns x 25 rows of text, or 320 x 200 dots in bitmap mode.
The five display modes and their control bits
Three bits across two registers select the mode. ECM=$D011 bit6, BMM (bitmap)
=$D011 bit5, MCM (multicolor)=$D016 bit4.
| Mode | ECM | BMM | MCM | Resolution / cell | Colors per cell |
|---|
| Standard text | 0 | 0 | 0 | 40x25 chars, 8x8 | 1 (per-cell from color RAM) + shared background |
| Multicolor text | 0 | 0 | 1 | 8x8, dots 2 wide | 3 shared ($D021/$D022/$D023) + 1 per-cell |
| Extended bg (ECM) | 1 | 0 | 0 | 40x25, 8x8 | 1 fg + 1 of 4 backgrounds ($D021–$D024) per char |
| Standard bitmap | 0 | 1 | 0 | 320x200 | 2 per 8x8 cell, both from screen RAM nibbles |
| Multicolor bitmap | 0 | 1 | 1 | 160x200 | 4 per 8x8 cell |
$D011 = 53265, $D016 = 53270. These are read-modify-write registers — always
preserve the other bits:
POKE 53265,PEEK(53265)OR 64 : REM ECM on ($D011 bit6)
POKE 53265,PEEK(53265)OR 32 : REM bitmap on ($D011 bit5)
POKE 53270,PEEK(53270)OR 16 : REM multicolor on ($D016 bit4)
POKE 53270,PEEK(53270)AND 239 : REM multicolor off
Assembly equivalents (set bitmap mode, keep other bits):
LDA $D011
ORA #$20 ; set BMM (bit 5)
STA $D011
ECM and MCM together (ECM+MCM, or ECM+BMM) select invalid/illegal modes
that blank to black — documented in c64-vic-ii.
Memory map: screen RAM, color RAM, character memory
| What | Default address | Notes |
|---|
| Screen RAM (char codes) | $0400–$07E7 (1024–2023), 1000 bytes | one screen-code byte per cell |
| Color RAM | $D800–$DBE7 (55296–56295), 1000 nibbles | 4-bit only, fixed location, never moves |
| Character ROM | $D000–$DFFF | 2 sets (uppercase/gfx + lowercase), under the I/O |
| Character generator base | default $1000 (ROM image) | set by $D018 |
| Border color | $D020 (53280) | |
| Background color #0 | $D021 (53281) | screen background |
Color RAM is only the low 4 bits at $D800 — you cannot store 8-bit values
there, and it is the same physical RAM regardless of video bank. Background
colors #1–#3 are $D022/$D023/$D024 (used by multicolor text and ECM).
$D018 — screen + character memory pointer (53272)
$D018 bits 7-4 : VM13-VM10 screen RAM base = (bits 7-4) * $0400 within bank
$D018 bits 3-1 : CB13-CB11 char memory base = (bits 3-1) * $0800 within bank
(in bitmap mode, bit 3 alone selects the $2000 bitmap base)
POKE 53272,(PEEK(53272)AND240)OR A : REM A picks SCREEN base, hi nibble
POKE 53272,(PEEK(53272)AND15) OR A : REM A picks CHAR base, low nibble
Char-memory A values (add the bank base): 0=$0000, 2=$0800, 4=$1000 ROM
image (default), 6=$1800 ROM image, 8=$2000, 10=$2800, 12=$3000, 14=$3800.
POKE 53272,(PEEK(53272)AND240)+12 is the standard "put my charset at 12288"
move. POKE 53272,21 restores the normal C64 setup.
Custom (programmable) characters
A character is 8x8 = 8 bytes (1 byte per row, MSB = leftmost pixel). A full
set is 256 chars x 8 = 2K (2048 bytes), and must start on a 2K boundary
(the $D018 low-nibble values above).
Steps in BASIC:
- Lower the top of BASIC to protect the charset (e.g.
POKE 52,48:POKE 56,48:CLR
to reserve from 12288 up).
- Point VIC at it:
POKE 53272,(PEEK(53272)AND240)+12 (charset at 12288).
- Copy any ROM chars you want to keep (the char ROM is under I/O — see Gotchas),
then POKE your 8-byte patterns: char N's rows live at
base + N*8 .. +7.
Compute a row byte from 8 pixels: b = b1*128 + b2*64 + ... + b8*1.
Video bank selection (CIA2 $DD00)
The VIC sees only 16K at a time. Bits 0–1 of CIA #2 port A ($DD00, 56576)
select which 16K bank — but the bits are inverted (value 3 = bank 0):
| $DD00 bits 1,0 | Bank | VIC range |
|---|
| 11 (POKE val 3) | 0 | $0000–$3FFF (default) |
| 10 (val 2) | 1 | $4000–$7FFF |
| 01 (val 1) | 2 | $8000–$BFFF |
| 00 (val 0) | 3 | $C000–$FFFF |
POKE 56578,PEEK(56578)OR 3 : REM make $DD00 bits 0,1 outputs
POKE 56576,(PEEK(56576)AND 252)OR A : REM A = value from table above
The character ROM image is only visible to the VIC in banks 0 and 2 (at
$1000 and $9000 respectively). In banks 1 and 3 you must supply your own charset
(or copy the ROM into bank RAM). All VIC base addresses ($D018, sprite pointers)
are relative to the selected bank's start.
Bitmap mode specifics
Standard hi-res bitmap: 8000 bytes (320x200 / 8). Color comes from screen RAM
(NOT color RAM): upper nibble = "1" pixel color, lower nibble = "0" pixel color,
per 8x8 cell.
Multicolor bitmap (160x200, 2-bit pixels) color sources per cell:
00 Background color #0 ($D021)
01 upper 4 bits of screen memory
10 lower 4 bits of screen memory
11 the color-RAM nibble ($D800+)
Set bitmap base with $D018 bit 3 (e.g. POKE 53272,PEEK(53272)OR 8 puts the
bitmap at offset $2000 in the bank). You must clear the 8K bitmap yourself
before drawing.
Smooth scrolling
The fine-scroll registers are the low 3 bits of $D011 (vertical) and $D016
(horizontal); they shift the whole screen 0–7 pixels. To scroll new data on you
shrink the visible area so the covered edge has room:
- 38-column mode: $D016 bit 3 = 0 (
POKE 53270,PEEK(53270)AND247) for
horizontal scroll — still 40 cols in RAM, only 38 shown.
- 24-row mode: $D011 bit 3 = 0 (
POKE 53265,PEEK(53265)AND247) for vertical.
POKE 53270,(PEEK(53270)AND 248)+X : REM X = 0..7 horizontal fine scroll
POKE 53265,(PEEK(53265)AND 248)+Y : REM Y = 0..7 vertical fine scroll
Loop the fine value 0→7, then do a full character-cell shift of screen RAM (in
machine language for speed) and reset the fine register. Exact raster-stable
scrolling lives in c64-vic-ii.
Quick answers
- Default screen RAM? $0400 (1024). Color RAM? $D800 (55296), 4-bit.
- Change border / background?
POKE 53280,c / POKE 53281,c, c = 0–15.
- Where's the charset normally? Char ROM imaged at $1000 in bank 0; the
default $D018 is $15 (21), and its char-base field selects that $1000 image
(bit 0 is unused).
- Why did my chars vanish after switching banks? The ROM charset image only
exists in banks 0 and 2; supply your own in banks 1/3.
Gotchas
- Color RAM is 4-bit nibbles at $D800 and is fixed — it does not move with
the screen or the bank. Don't expect to read back a full byte.
- The character ROM is "under" the I/O at $D000–$DFFF — the source notes it
"begins at location 53248 ($D000) when the I/O is switched off." To copy it
from the CPU you must bank the I/O block out via the $0001 processor port (and
disable interrupts while it's out); see c64-memory-map for the exact
banking POKEs. The VIC always sees the ROM image at $1000/$9000 in banks 0/2
regardless of CPU banking.
- $DD00 bank bits are inverted (3 = bank 0). And you must set them as outputs
in $DD02 first.
- Always read-modify-write $D011 and $D016 — they pack mode bits, the fine-scroll
bits, the 24/25-row and 38/40-col bits, and raster bit 8 together.
- Sprite pointers sit at the end of screen RAM ($07F8 for the default screen);
moving the screen moves them too — see c64-sprites.
How to read the references
references/graphics-programming.md — the Programmer's Reference Guide
Chapter 3 graphics half, verbatim: every mode, full char-memory and bank
tables, the worked custom-character and bitmap BASIC programs, and the smooth-
scroll walkthrough. Read this for the authoritative POKE values and listings.references/color-graphics-tutorial.md — the User's Guide Chapter 5
gentle tutorial (PRINTing colors, CHR$ color codes, POKEing the screen,
bouncing-ball example). Read this when you want the beginner-level framing.references/screen-color-memory-map.md — App D screen and color memory
maps with the address-of-each-row diagrams and the 16 color codes. Read when
you need the exact address of a screen/color cell.references/vic-register-map.md — App G VIC register map ($D000–$D02E)
as a convenience copy. The deep, cycle-exact reference is c64-vic-ii;
start there for anything timing-related.
