DECSET 1 — DECCKM (application cursor keys)

CSI ? 1 h (DECCKM set) switches the cursor (arrow) keys into 'application' mode: they send SS3-prefixed sequences (ESC O A/B/C/D) instead of the normal CSI forms (ESC [ A/B/C/D). CSI ? 1 l restores normal mode. Full-screen programs enable it so arrow keys are unambiguous.

terminal-dec-private-mode kind control-sequence status standard verification verified tier B terminal-escape@1

aka: DECCKM · application cursor keys · DECSET 1 · ?1h / ?1l · cursor key mode

frame

DEC-private-mode introducer: \x1b[? ESC [ ? (0x1B 0x5B 0x3F)

terminator (none): ST · BEL

parameters / subcommands

id	name	bytes (ST)	meaning
set	Enable (DECSET)	\x1b[?1h	CSI ? 1 h sets DECCKM: arrow keys now send SS3 sequences, e.g. Up = ESC O A (\x1bOA) rather than ESC [ A.
reset	Disable (DECRST)	\x1b[?1l	CSI ? 1 l clears DECCKM: arrow keys send the normal CSI sequences ESC [ A/B/C/D.

gotchas

In APPLICATION mode arrow keys are ESC O A..D (SS3); in NORMAL mode they are ESC [ A..D (CSI). A key-parser must know the current mode or read both.
Many TUIs enable DECCKM via terminfo (smkx) on entry and disable it (rmkx) on exit; if your program crashes without resetting, the shell's arrow keys can misbehave until reset.
DECCKM affects only the cursor (arrow) keys, not the numeric keypad (that is DECKPAM/DECKPNM).
The SS3 prefix is ESC O (0x1B 0x4F), not ESC [ — easy to confuse when matching byte patterns.
Always pair set on entry with reset on exit (or rely on terminfo smkx/rmkx).

provenance

source: https://invisible-island.net/xterm/ctlseqs/ctlseqs.html
version: xterm ctlseqs, patch #410, 2026/04/19
retrieved: 2026-05-29 · updated: 2026-05-29T00:00:00Z

per-fact attribution:

#summary — https://invisible-island.net/xterm/ctlseqs/ctlseqs.html xterm ctlseqs: Ps = 1 -> Application Cursor Keys (DECCKM). When set, cursor keys send ESC O x (SS3) instead of ESC [ x.
ext.params — https://vt100.net/docs/vt510-rm/DECCKM.html DEC VT510 manual: DECCKM (mode 1) selects application vs normal cursor-key sequences.

DECSET 1 — DECCKM (application cursor keys)

frame

parameters / subcommands

gotchas

provenance

see also