| name | c64 |
| description | Orientation and router for Commodore 64 programming and hardware — the architecture at a glance, the memory/IO map, and a "which skill answers this" index across the focused c64-* skills (BASIC, graphics, sprites, VIC-II, SID, 6510 assembly, KERNAL, memory map, CIA, I/O, disk, tape, game ports, PETSCII, keyboard, hardware, disassembly). Use this skill WHEN a C64 question is broad, vague, or cross-cutting ("how does the C64 work", "where do I start", "what chip does sound"), when you need the high-level memory map or chip locations, or to route a specific question to the right c64-* skill. For depth, defer to the specific sibling skill. |
Commodore 64 — overview & router
The C64 (1982, ~17M sold) is a 6510-based 8-bit home computer: 64 KB RAM, a
VIC-II video chip, a SID sound chip, two CIA I/O chips, and BASIC + KERNAL in ROM.
This skill is the map of the territory and a router to the focused c64-*
skills. Use it to orient, then open the specific skill for depth.
The machine in one screen
| Part | Chip | Job | Lives at | Skill |
|---|
| CPU | 6510 (6502 + I/O port) | runs code; $00/$01 bank ROM/RAM | — | c64-assembly |
| Video | VIC-II 6567(NTSC)/6569(PAL) | screen, sprites, raster, IRQ | $D000-$D3FF | c64-vic-ii, c64-graphics, c64-sprites |
| Sound | SID 6581 | 3-voice synth + filter | $D400-$D7FF | c64-sid |
| I/O #1 | CIA1 6526 | keyboard, joysticks, timer IRQ | $DC00-$DCFF | c64-cia, c64-keyboard, c64-game-ports |
| I/O #2 | CIA2 6526 | serial bus, user port, VIC bank, NMI | $DD00-$DDFF | c64-cia, c64-io |
| Banking | PLA 82S100 | decodes ROM/RAM/IO/charROM | — | c64-memory-map, c64-hardware |
| Firmware | BASIC + KERNAL ROM | language + OS routines | $A000,$E000 | c64-basic, c64-kernal |
Memory map at a glance
$0000-$00FF zero page ($00/$01 = 6510 bank-switch port)
$0100-$01FF CPU stack
$0200-$03FF OS work area + buffers (IRQ vector $0314, tape buffer $033C)
$0400-$07FF default screen RAM (sprite pointers $07F8-$07FF)
$0800-$9FFF BASIC program / free RAM (BASIC starts $0801)
$A000-$BFFF BASIC ROM (or RAM, switchable)
$C000-$CFFF free RAM (4K) — favourite spot for ML
$D000-$DFFF I/O: VIC $D000 / SID $D400 / colorRAM $D800 / CIA1 $DC00 / CIA2 $DD00
(or character ROM, or RAM — depends on $01)
$E000-$FFFF KERNAL ROM (or RAM); jump table $FF81-$FFF3
Full detail, the $01 banking-bit table, and the PLA logic → c64-memory-map.
Which skill answers this?
| You want to… | Skill |
|---|
| write/understand BASIC; a keyword's syntax | c64-basic |
| print special chars, color/cursor codes, build a text UI | c64-petscii |
| know what a key does (C=, RUN/STOP, RESTORE), use the editor | c64-keyboard |
| draw chars/bitmaps, set screen colors, scroll, custom fonts | c64-graphics |
| make/move/collide sprites | c64-sprites |
| exact raster timing, bad lines, all video modes, demo effects | c64-vic-ii |
| produce sound/music, program the SID | c64-sid |
| write 6510 machine language; call ML from BASIC | c64-assembly |
| call OS routines (print, load, save, input) | c64-kernal |
| the full memory map / banking / where things live | c64-memory-map |
| timers, IRQ/NMI, the chip behind keyboard/joystick/serial | c64-cia |
| files & devices, serial bus, printer, modem, RS-232, user/cartridge port | c64-io |
| disk drive: load, save, directory, DOS commands | c64-disk |
| cassette / Datasette load, save, "directory" | c64-tape |
| read joysticks, paddles, light pen | c64-game-ports |
| repair, pinouts, voltages, board revisions, chips | c64-hardware |
| reverse-engineer a .prg / dump / listing | c64-disassembly |
Quick answers to common questions
- Which control port is "player 1"? Hardware: port 1 reads at CIA1
$DC01,
port 2 at $DC00. By software convention most single-joystick games use
control port 2. Detail → c64-game-ports.
- What does the C= (Commodore) key do? With SHIFT it toggles the
upper-case/graphics vs upper/lower-case character set; held with a number key it
selects one of the second set of text colors; it can also slow listings. →
c64-keyboard.
- How do I see a disk directory?
LOAD"$",8 then LIST. → c64-disk.
- How do I list a tape "directory"? Tape is sequential — there is no
random-access directory; you search forward for files. → c64-tape.
- How do I clear the screen / where is screen RAM?
PRINT CHR$(147) (or
POKE screen codes to $0400-$07FF, colors to $D800). → c64-petscii,
c64-graphics.
- Where do I put a machine-language routine?
$C000 (free 4K) or the tape
buffer $033C; call with SYS. → c64-assembly.
- PAL vs NTSC? PAL = 6569 (50 Hz, 63 cycles/line, 312 lines); NTSC = 6567
(60 Hz, ~64–65 cycles/line, 262/263 lines). Matters for timing/music. →
c64-vic-ii.
How to use the set
Each c64-* skill is self-contained and carries the relevant sliced reference
docs under its own references/. Start here for orientation or a one-liner; jump
to the specific skill for register layouts, code, and exact behavior. For generic
6502/65C02/65816 CPU semantics beyond the C64's 6510, the optional companion repo
https://github.com/sunsided/6502-skills pairs well — not required.
