KAM Keyboard Action Mode
Lock and unlock the keyboard.
CSI 2 h/l
- ECMA-48
- §7.2.11 KAM – Keyboard Action Mode, p. 24
- DEC STD 070
- §5.10.1.1 ANSI Specified Modes, p. 5-133
- VT220
- §4.6.3 Keyboard Action Mode (KAM)
- VT510
- KAM—Keyboard Action Mode
- xterm
- Functions using CSI
Mode 2 locks the keyboard. Set (CSI 2 h), the keyboard sends nothing to the host; reset (CSI 2 l), which is the default, it works as usual.
| State | ECMA-48 calls it | Meaning |
|---|---|---|
Reset, CSI 2 l | ENABLED | the keyboard can be used |
Set, CSI 2 h | DISABLED | all or part of the keyboard cannot be used |
DEC STD 070 lists it among the ANSI modes a DEC terminal accepts, and its keyboard chapter (p. 6-37) says that when it is locked all but the local function keys F1 to F5 are disabled. The VT510 manual adds that the terminal shows its Wait indicator, and that Set-Up and the session key still work.
xterm keeps the mode, and while it is set it ignores what is typed (input.c). It changes only what the keyboard sends, which this site cannot press, so nothing on the screen changes. libghostty-vt keeps the mode too, and both answer DECRQM with its state.
Support
| Terminal | Version | Support | Notes |
|---|---|---|---|
| VT220 | manual, 2nd ed., 1984 | Yes | §4.6.3 Keyboard Action Mode (KAM) |
| VT510 | manual, 1st ed., 1993 | Yes | KAM |
| xterm | patch 412, xterm-411a | Yes | |
| libghostty-vt | 0f171f6 | Yes | |
| kitty | 0.49.1, run in a VM | No | fails the 3 cases that show it working |
| foot | 1.28.0, run in a VM | No | fails the 3 cases that show it working |
| xterm.js headless | 6.0.0, run as a library | No | fails the 3 cases that show it working |
| alacritty_terminal | 0.26.0, run as a library | No | fails the 3 cases that show it working |
| ConEmu | build 230724, its documentation | No | not in its ANSI escape codes |
| rxvt-unicode | 9.31, run in a VM | No | fails the 3 cases that show it working |
| VTE | 0.84.1, run as a library | No | fails the 3 cases that show it working |
Validation
KAM-1: Reset by default
\e[2$p
|_____|
reply \e[2;2$y
KAM-2: Set
\e[2h
\e[2$p
|_____|
reply \e[2;1$y
KAM-3: And reset again
\e[2h
\e[2l
\e[2$p
|_____|
reply \e[2;2$y
KAM-4: Nothing on the screen changes
A
\e[2h # lock the keyboard
B
\e[2l
C
|ABC__|
cursor 1,4