c64-keyboard

name

c64-keyboard

description

The C64 keyboard and screen editor: every special key and what it does — the Commodore (C=) key, CTRL, RUN/STOP, RESTORE, SHIFT / SHIFT-LOCK, CLR/HOME, INST/DEL, cursor (CRSR) keys, function keys f1–f8, RETURN — plus screen-editor behavior (quote mode, insert mode, full-screen line editing, the 10-key buffer). Use this skill WHEN asked "what does the C= key do", "switch to lower case", "what is RUN/STOP + RESTORE", "clear the screen", "what's quote mode", "type a cursor-down into a string", "reset the C64", or about the f-keys. Pairs with c64-petscii and c64-cia (the NMI/RESTORE mechanism).

The Commodore 64 Keyboard & Screen Editor

The C64 keyboard is an 8×8 switch matrix scanned by the KERNAL via CIA #1 ($DC00 columns / $DC01 rows). Keystrokes queue in a 10-character buffer (type-ahead) and are decoded into PETSCII in that buffer. The matrix code of the key held now sits at location 197 ($C5) — PEEK(197) returns it (64 = none). The buffer itself is at 631–640 with its count at 198; you can stuff keys there.

Special keys — what each does

Key	Effect
RETURN	Enters the current logical (up to 80-char) line; the editor reads & tokenizes it.
SHIFT	Upper case in lower/upper mode; the right-front graphic in upper/graphics mode; the shifted function (f2/f4/f6/f8) on the function keys.
SHIFT LOCK	Mechanical latch holding SHIFT down.
C= (Commodore)	See below — charset toggle (with SHIFT) and second color set (with number keys), and the left-front graphic (with a graphic key).
CTRL	Held with a number key 1–8 sets text color; with 9/0 turns ReVerSe on/off; held during LIST slows the listing. Emits the PETSCII color/RVS control codes.
RUN/STOP	Interrupts (breaks) a running BASIC program → BREAK, and halts a LIST (it stops the listing — it does not slow it; that's CTRL). With SHIFT+RUN/STOP: LOAD+RUN first program from tape.
RUN/STOP + RESTORE	Warm reset: clears screen, restores default I/O & screen state, leaves the BASIC program intact. (RESTORE drives the CPU NMI line.)
RESTORE	On its own does little; held-down RUN/STOP makes the NMI restore the machine to its normal state.
CLR/HOME	HOME = cursor to top-left (no erase). SHIFT+CLR/HOME = clear screen + home.
INST/DEL	DEL = backspace, delete char to the left, close the gap. SHIFT+INST/DEL = INSerT a space at the cursor.
CRSR ↑↓ / CRSR ←→	Two cursor keys: unshifted move down / right, SHIFTed move up / left. Auto-repeat while held.
f1–f8	Four physical keys; f1/f3/f5/f7 unshifted, f2/f4/f6/f8 shifted. Not bound by default — read them via GET/CHR$(133..140) and act on them.

"What does the C= key do?" (the common question)

The Commodore key has three jobs:

1. C= + SHIFT toggles the two character sets — upper-case/graphics ↔ upper/lower case. (Same as POKE 53272,21 / POKE 53272,23 from BASIC.)
2. C= + a number key (1–8) selects the second set of 8 text colors (CTRL + number gives the first 8).
3. C= + a graphics key prints the graphic on the left front of that key (SHIFT prints the right-front graphic).

Resetting the machine

• Warm reset, keep program: hold RUN/STOP, press RESTORE.
• Cold reset (wipes program/data): SYS 64738.

Charset / color quick recipes

POKE 53272,23 : REM switch to lower/upper case set (set 2)
POKE 53272,21 : REM switch back to upper case/graphics (set 1)
PRINT CHR$(28) : REM red text (CTRL+3 equivalent)   -- color CHR$ codes -> c64-petscii

The screen editor

Full-screen, line-oriented editor over an 80-char logical line (two 40-col physical rows). LIST a line, move the cursor anywhere on it, change it, press RETURN — the whole logical line is re-read, so you don't retype it. Change just the line number and RETURN to duplicate a line. Editing a line longer than 80 chars loses the overflow (the editor reads only two physical rows) — the same reason INPUT is capped near 80 chars.

Quote mode

Entered automatically when the cursor is to the right of an odd number of ". In quote mode the cursor/color control keys no longer move the cursor; instead they insert a reversed glyph standing for that control code, so you can embed cursor-positioning and color changes inside a string literal. Those codes then execute when the string is PRINTed.

• DEL is the only control NOT trapped by quote mode.
• Cancel quote mode with RETURN, or RUN/STOP + RESTORE.

10 PRINT"A{CRSR R}{CRSR R}B"   : REM the {CRSR R} are reversed glyphs typed in quote mode

Insert mode

SHIFT+INST/DEL opens space and enters INSERT mode until the opened space is filled. In insert mode, control keys also show as reversed glyphs — but here INST inserts real spaces and DEL makes a reversed T, which lets you put DEL characters into a PRINT string (impossible in quote mode). Cancel with RETURN, SHIFT+RETURN, RUN/STOP+RESTORE, or by filling the inserted spaces.

The keyboard buffer (type-ahead)

Up to 10 keystrokes queue while the machine is busy; an 11th+ is dropped. Because a queued RETURN commits everything before it, flush stray input before a prompt:

10 GET JUNK$: IF JUNK$<>"" THEN 10 : REM empty the keyboard buffer

How to read the references

• references/keyboard-and-editor.md — PRG Ch2 verbatim: the keyboard buffer, the 8×8 matrix and how the KERNAL scans it (CIA #1 $DC00/$DC01, location 197), POKEing the buffer (631–640 / 198), and the full Screen Editor section — quote mode, insert mode, the Table 2-2 cursor-control glyphs, and the printable special characters. Read for the authoritative editor behavior.
• references/keyboard-tutorial.md — User's Guide verbatim: a friendly walk-through of each key (RETURN, SHIFT, CRSR, INST/DEL, CLR/HOME, RESTORE, CTRL, RUN/STOP, the C= key, function keys), the CTRL-for-color intro, and the "back to normal" reset tips (RUN/STOP+RESTORE, SYS 64738). Read for plain per-key explanations.

Cross-links

• The actual PETSCII codes these keys emit (cursor, color, RVS, f-key CHR$ values) and the screen/POKE codes → c64-petscii.
• The NMI line that RESTORE pulls, and CIA #1's role in scanning the matrix → c64-cia.