DEC Private Modes

Terminals have a number of virtual toggle switches called "modes" which change how the terminal behaves. DEC added its own "private" (non-standard) modes accessible using the sequence prefix Esc [ ?.

For example, setting mode #3 high will switch the terminal to display 132 columns and resetting it low will switch the terminal back to 80 columns.

• Esc [ ? 3 h 132-column mode
• Esc [ ? 3 l 80-column mode (that's an "L" as in "low")
• Esc [ ? 3 $ p Prints the status of private mode #3.

See the script checkmode to check what private modes are available on your terminal.

Supported by the VT340

DEC Private Modes available on the VT340.

Note 1: For a few modes, hackerb9 suggests configuring your VT340 (using the Set-Up button) differently than the factory default.

Note 2: Logging into a UNIX system may change some of these settings from the power on defaults via the terminfo "reset" sequence. (Try TERM=vt340 tput reset | cat -v to check.)

Mode	Description	VT340 default	hackerb9 suggests	Terminfo reset	Notes
1	Application Cursor Key Mode (DECCKM), VT100.	reset		set	When SET, arrow keys send special application commands to the host
2	ANSI/VT52 Mode (DECANM), VT100.	set			RESET to enter VT52 mode. To leave VT52 mode, use Esc <.
3	132 Column Mode (DECCOLM), VT100.	reset		reset	VT340 docs claim DECCOLM is deprecated in favor of DECSCPP (CSI 132 $ ¦). However, DECSCPP sets the columns per page, not screen. Unlike DECCOLM, DECSCPP does not change the visible number of columns on the screen; instead DECSCPP requires horizontal scrolling (see mode 60, DECHCCM). On the VT5x0, see mode 95 (DECNCSM) to prevent the page from being cleared by DECCOLM.
4	Smooth (Slow) Scroll (DECSCLM), VT100.	set	reset	reset	On the VT340 and possibly other terminals, this option is not binary. In the SetUp menu, scrolling can be 'Jump' (same as RESET), or 'Smooth-1', '-2', or '-4' which scroll by scanlines instead of character cells. The VT340 factory default is 'Smooth-2', which is 25 scanlines (2.5 text lines) per second. Smooth-1 is half and Smooth-4 is twice the speed. If any of the Smooth options are selected, then the result from DECRQM (Request DEC Private Mode) will show mode 4 as SET. However, when mode 4 is SET using DECSET (CSI ? 4 h), the VT340 always selects Smooth-2. See also the VT5x0's DECSSCLS (Set Scroll Speed, CSI Ps SP p).
5	Reverse Video Screen (DECSCNM), VT100.	reset		reset	SET is light bg, RESET is dark bg.
6	Origin Mode (DECOM), VT100.	reset
7	Auto-Wrap Mode (DECAWM), VT100.	reset	set	set	When RESET, cursor will not advance beyond right-most column. When SET characters beyond the last column will be printed on the next line.
8	Auto-Repeat Keys (DECARM), VT100.	set		set
10	Edit Mode (DECEDM).	reset
11	Line Transmit Mode (DECLTM).	reset
13	Space compression field delimiter (DECSCFDM)	reset
14	Transmit execution (DECTEM).	set
16	Edit key execution (DECEKEM).	set			When SET, Shift+Edit on the VT340 switches immediately between interactive and edit mode. When RESET, the terminal sends DECEDM to the host to switch modes and waits for the host return DECEDM before changing the terminal's local editing mode.
18	Print Form Feed (DECPFF), VT220.	reset			When SET, the terminal sends a form feed (FF) to the printer at the end of a printing function. The default, RESET, is to send to nothing. DECPFF does not affect the Print Cursor Line function.
19	Set printer extent to full screen (DECPEX), VT220.	set			When RESET, the print page function only prints the scrolling region (data inside the margins).
25	Text cursor enable (DECTCEM), VT220.	set
38	Tektronix mode (DECTEK), VT240, xterm.	reset
42	National Replacement Character sets (DECNRCM), VT220.	permanently reset			On the VT340 and perhaps other terminals, DECNRCM is PERMANENTLY RESET when the Keyboard Dialect selected in the Set Up menu is 'North American'.
43	Graphics Expanded Print Mode (DECGEPM).	reset
44	Graphics Print Color (DECGPCM)	reset	set
45	Graphics Print Color Syntax (DECGPCS).	reset	set
46	Graphics Print Background (DECGPBM).	set
47	Graphics Rotated Print Mode (DECGRPM).	reset
53	VT131 transmit (DEC131TM).	reset			For local editing, if both the Line Transmit Mode (DECLTM) and the Transmit Termination Mode (ANSI TTM) are RESET, then this mode controls the character block size. If SET, use VT131 partial page (last marker to cursor). If RESET, use ANSI partial page (selected text)."
60	Horizontal cursor coupling (DECHCCM).	reset
61	Vertical cursor coupling (DECVCCM).	set
64	Page cursor coupling (DECPCCM).	set
66	Application/Numeric keypad mode (DECNKM), VT320	reset
67	Backarrow key sends backspace (DECBKM), VT340, VT420, VT520.	reset			When RESET (the default), backarrow key sends delete.
68	Keyboard Usage: Data Processing or Typewriter Keys (DECKBUM).	reset			Data Processing characters are printed on the right half of the keycaps. According to ek-520-rm, 'If you use the North American language, then DECKBUM should always be RESET (typewriter). For all other languages, you can use either mode.'
73	Transmit rate limiting (DECXRLM).	set
80	Sixel Display Mode (DECSDM).	reset

Not recognized on the VT340

Private Modes known to the checkmode program, but unavailable on the VT340.

Mode	Description	Notes
0	Invalid mode	Use of mode #0 is an error and always ignored.
9	Send Mouse X & Y on button press, X10 XTerm.	VT100 used mode 9 for interlace, but dropped it in VT200+.
12	Katakana Shift Mode (DECKANAM), VT382-J
20	Overstrike Mode (OS), VK100.
21	Local BASIC Mode (BA), VK100.
22	Host BASIC Mode (BA), VK100.
23	Programmed Keypad Mode (PK), VK100.
24	Auto Hardcopy Mode (AH), VK100.
27	Proportional Spacing, printers.
29	Pitch Select Mode, printers.
30	Show scrollbar, rxvt.
34	Cursor direction, right to left.
35	Hebrew keyboard mapping.	ek-vt3xx-tp is in error. DECTEK is actually 38.
36	Hebrew encoding mode.
40	Carriage Return/New Line Mode (DECCRNLM), printers.	Allow DECCOLM (mode 3) to switch columns.
41	Unidirectional Print Mode (DECUPM), printers.	Bidirectional when RESET.
49	Thai Keyboard Input Mode (DECTHAIM), VT382-T
50	Thai Cursor Mode (DECTHAICM), VT382-T	SET is internal cursor, RESET is physical cursor
57	North American / Greek keyboard mapping (DECNAKB)
58	IBM ProPrinter Emulation (DECIPEM)	Interpret subsequent data according to the IBM ProPrinter protocol syntax instead of the DEC protocol.
59	Kanji/Katakana Display Mode (DECKKDM), VT382-J
69	Vertical split screen / Left and right margin mode (DECVSSM/DECLRMM), VT420 and up.
81	Keyboard sends key position reports instead of character codes (DECKPM).
90	Thai Space Compensating Mode (DECTHAISCM), VT382-T
95	Do not clear screen when DECCOLM is set/reset (DECNCSM), VT510 and up.
96	Perform a copy/paste from right-to-left (DECRLCM), VT520	Only valid with Hebrew keyboard language, see DEC mode 35
97	CRT Save Mode (DECCRTSM), VT520
98	Auto-resize the number of lines-per-page when the page arrangement changes (DECARSM), VT520
99	Modem Control Mode: require DSR or CTS before communicating (DECMCM), VT520
100	Send automatic answerback message 500ms after a communication line connection is made (DECAAM), VT520
101	Conceal Answerback Message (DECCANSM), VT520
102	Discard NUL characters upon receipt, or pass them on to the printer (DECNULM)
103	Half-Duplex Mode (DECHDPXM), VT520
104	Enable Secondary Keyboard Language (DECESKM), VT520
106	Overscan mode for monochrome VT520 terminal (DECOSCNM)
108	Num Lock Mode of keyboard (DECNUMLK)
109	Caps Lock Mode of keyboard (DECCAPSLK)
110	Keyboard LED's Host Indicator Mode (DECKLHIM)
111	Framed Windows with title bars, borders, and icons (DECFWM), VT520
112	Allow user to Review Previous Lines that have scrolled off the top (DECRPL)
113	Host Wake-up Mode, CRT and Energy Saver (DECHWUM), VT520
114	Use an alternate text color for underlined text (DECATCUM), VT520
115	Use an alternate text color for blinking text (DECATCMB), VT520
116	Bold and blink styles affect background as well as foreground (DECBSM), VT520
117	Erase Color is screen background (VT) or text background (PC) (DECECM), VT520	Background color used when text is erased or new text is scrolled on to the screen
1000	Send Mouse X & Y on button press and release. (X11 XTerm mouse).
1001	Use Hilite Mouse Tracking, xterm.
1002	Use Cell Motion Mouse Tracking, xterm.
1003	Use All Motion Mouse Tracking, xterm.
1004	Send FocusIn/FocusOut events, xterm.
1005	UTF-8 Mouse Mode, xterm.
1006	SGR Mouse Mode, xterm.
1007	Alternate Scroll Mode, xterm.
1010	Scroll to bottom on tty output, rxvt.
1011	Scroll to bottom on key press, rxvt.
1015	Urxvt Mouse Mode, rxvt.
1016	SGR Mouse PixelMode, xterm.
1021	High intensity bold/blink color, rxvt.
1034	Interpret 'Meta' key, xterm.	This sets the eighth bit of keyboard input.
1035	Enable special modifiers for Alt and NumLock keys, xterm.
1036	Send ESC when Meta modifies a key, xterm.
1037	Send DEL from the editing-keypad Delete key, xterm.
1039	Send ESC when Alt modifies a key, xterm.
1040	Keep selection even if not highlighted, xterm.
1041	Use the CLIPBOARD selection, xterm.
1042	Enable Urgency windowmanager hint when Control-G received, xterm.
1043	Enable raising of the window when Control-G is received, xterm.
1044	Reuse the most recent data copied to CLIPBOARD, xterm
1046	Enable switching to/from Alternate Screen Buffer, xterm.
1047	Use Alternate Screen Buffer, xterm.
1048	Save cursor as in DECSC, xterm.
1049	Save cursor as in DECSC, switch to the Alternate Screen Buffer.
1050	Set terminfo/termcap function-key mode, xterm.
1051	Set Sun function-key mode, xterm.
1052	Set HP function-key mode, xterm.
1053	Set SCO function-key mode, xterm.
1060	Set legacy keyboard emulation, i.e, X11R6, xterm.
1061	Set VT220 keyboard emulation, xterm.
1070	Use private color registers for each graphic, xterm.	When SET, each Sixel/ReGIS graphic gets a fresh palette. When RESET, colormap changes persist just like on a true VT340. SET is the default for XTerm.
2004	Set bracketed paste mode, xterm.
2026	Synchronized output. iTerm2, Contour, Kitty.	When SET, new data is not displayed until the mode is RESET. Can be used by applications for double-buffering & page flipping to prevent screen tearing.
8452	Sixel leaves cursor right of image, RLogin, xterm.

No undocumented private modes

Using checkmode --trawl, private modes 0 to 9999 were queried and hackerb9's VT340 replied "not recognized" for any numbers not listed in the documentation.