Quick Reference

• Communication UART (Rx, Tx) can be configured in the System Settings.
• Boot log and debug messages are available on pin GPIO2 (P2) at 115200 baud, 1 stop bit, no parity. Those messages may be disabled through compile flags.
• Loopback test: Connect the Rx and Tx pins with a piece of wire. Anything you type in the browser should appear on the screen. Set Parser Timeout = 0 in Terminal Settings to be able to manually enter escape sequences.
• There is very little RAM available to the webserver, and it can support at most 4 connections at the same time. Each terminal session (open window with the terminal screen) uses one persistent connection for screen updates. Avoid leaving unused windows open, or either the RAM or connections may be exhausted.
• For best performance, use the module in Client mode (connected to external network) and minimize the number of simultaneous connections. Enabling AP consumes extra RAM because the DHCP server and Captive Portal DNS server are started.
• In AP mode, check that the WiFi channel used is clear; interference may cause flaky connection. A good mobile app to use for this is WiFi Analyzer (Google Play). Adjust the hotspot strength and range using the Tx Power setting.
• Hold the BOOT button (GPIO0 to GND) for ~1 second to force enable AP. Hold it for ~6 seconds to restore default settings. (This is indicated by the blue LED rapidly flashing). Default settings can be overwritten in the System Settings.

ESPTerm emulates VT102 (pictured) with some additions from later VT models and Xterm. All commonly used attributes and commands are supported. ESPTerm is capable of displaying ncurses applications such as Midnight Commander using agetty.

ESPTerm accepts UTF-8 characters received on the communication UART and displays them on the screen, interpreting some codes as Control Characters. Those are e.g. Carriage Return (13), Line Feed (10), Tab (9), Backspace (8) and Bell (7).

Escape sequences start with the control character ESC (27), followed by any number of ASCII characters forming the body of the command.

Nomenclature & Command Types

Examples on this help page use the following symbols for special characters and command types:
(spaces are for clarity only, DO NOT include them in the commands!)

There are also some other commands that don't follow the CSI, SGR or OSC pattern, such as \e7 or \e#8. A list of the most important escape sequences is presented in the following sections.

The initial screen size, title text and button labels can be configured in Terminal Settings.

Screen updates are sent to the browser through a WebSocket after some time of inactivity on the communication UART (called "Redraw Delay"). After an update is sent, at least a time of "Redraw Cooldown" must elapse before the next update can be sent. Those delays are used is to avoid burdening the server with tiny updates during a large screen repaint. If you experience issues (broken image due to dropped bytes), try adjusting those config options. It may also be useful to try different baud rates.

UTF-8 support

ESPTerm supports all UTF-8 characters, but to reduce the screen buffer RAM size, only a small amount of unique multi-byte characters can be used at the same time (up to 160, depending on compile flags). Unique multi-byte characters are stored in a look-up table and are removed when they are no longer used on the screen. In rare cases it can happen that a character stays in the table after no longer being used (this can be noticed when the table fills up and new characters are not shown correctly). This is fixed by clearing the screen (\e[2J or \ec).

Keyboard

The user can input text using their keyboard, or on Android, using the on-screen keyboard which is open using a button beneath the screen. Supported are all printable characters, as well as many control keys, such as arrows, Ctrl+letters and function keys. Sequences sent by function keys are based on VT102 and Xterm.

The codes sent by Home, End, F1-F4 and cursor keys are affected by various keyboard modes (Application Cursor Keys, Application Numpad Mode, SS3 Fn Keys Mode). Some can be set in the Terminal Settings, others via commands.

Here are some examples of control key codes:

Key	Code	Key	Code
Up	\e[A, \eOA	F1	\eOP, \e[11~
Down	\e[B, \eOB	F2	\eOQ, \e[12~
Right	\e[C, \eOC	F3	\eOR, \e[13~
Left	\e[D, \eOD	F4	\eOS, \e[14~
Home	\eOH, \e[H, \e[1~	F5	\e[15
End	\eOF, \e[F, \e[4~	F6	\e[17~
Insert	\e[2~	F7	\e[18~
Delete	\e[3~	F8	\e[19~
Page Up	\e[5~	F9	\e[20~
Page Down	\e[6~	F10	\e[21~
Enter	\r (13)	F11	\e[23~
Ctrl+Enter	\n (10)	F12	\e[24~
Tab	\t (9)	ESC	\e (27)
Backspace	\b (8)	Ctrl+A..Z	ASCII 1-26

Action buttons

The blue buttons under the screen send ASCII codes 1, 2, 3, 4, 5, which incidentally correspond to Ctrl+A,B,C,D,E. This choice was made to make button press parsing as simple as possible.

Mouse

ESPTerm implements standard mouse tracking modes based on Xterm. Mouse tracking can be used to implement powerful user interactions such as on-screen buttons, draggable sliders or dials, menus etc. ESPTerm's mouse tracking was tested using VTTest and should be compatible with all terminal applications that request mouse tracking.

Mouse can be tracked in different ways; some are easier to parse, others more powerful. The coordinates can also be encoded in different ways. All mouse tracking options are set using option commands: CSI ? n h to enable, CSI ? n l to disable option n.

Mouse Tracking Modes

All tracking modes produce three numbers which are then encoded and send to the application. First is the event number N, then the X and Y coordinates, 1-based.

Mouse buttons are numbered: 1=left, 2=middle, 3=right. Wheel works as two buttons (4 and 5) which generate only press events (no release).

Mouse Report Encoding

The following encoding schemes can be used with any of the tracking modes (except Focus tracking, which is not affected).

ESPTerm implements Alternate Character Sets as a way to print box drawing characters and special symbols. A character set can change what each received ASCII character is printed as on the screen (eg. "{" is "π" in codepage 0). The implementation is based on the original VT devices.

Since ESPTerm also supports UTF-8, this feature is the most useful for applications which can't print UTF-8 or already use alternate character sets for historical reasons.

Supported codepages

• B - US ASCII (default)
• A - UK ASCII: # replaced with £
• 0 - Symbols and basic line drawing (standard DEC alternate character set)
• 1 - Symbols and advanced line drawing (based on DOS codepage 437, ESPTerm specific)

All codepages use codes 32-127, 32 being space. A character with no entry in the active codepage stays unchanged.

Codepage 0

Codepage 1

Codepage switching commands

There are two character set slots, G0 and G1. Those slots are selected as active using ASCII codes Shift In and Shift Out (those originally served for shifting a red-black typewriter tape). Often only G0 is used for simplicity.

Each slot (G0 and G1) can have a different codepage assigned. G0 and G1 and the active slot number are saved and restored with the cursor and cleared with a screen reset (\ec).

The following commands are used:

Code	Meaning
\e(x	Set G0 = codepage x
\e)x	Set G1 = codepage x
SO (14)	Activate G0
SI (15)	Activate G1

All text attributes are set using SGR commands like \e[1;4m, with up to 10 numbers separated by semicolons. To restore all attributes to their default states, use SGR 0: \e[0m or \e[m.

Those are the supported text attributes SGR codes:

Style	Enable	Disable
Bold	1	21, 22
Faint	2	22
Italic	3	23
Underlined	4	24
Striked	9	29
Overline	53	55
Blink	5	25
Inverse	7	27
𝔉𝔯𝔞𝔨𝔱𝔲𝔯	20	23
Conceal1	8	28

¹Conceal turns all characters invisible.

Colors are set using SGR commands (like \e[30;47m). The following tables list the SGR codes to use. Selected colors are used for any new text entered, as well as for empty space when using clearing commands (except screen reset \ec, which first clears all style attriutes. The configured default colors can be restored using SGR 39 for foreground and SGR 49 for background.

The actual color representation of the basic 16 colors depends on a color theme which can be selected in Terminal Settings.

Foreground colors

Background colors

256-color palette

ESPTerm supports in total 256 standard colors. The dark and bright basic colors are numbered 0-7 and 8-15. To use colors higher than 15 (or 0-15 using this simpler numbering), send CSI 38 ; 5 ; n m, where n is the color to set. Use CSI 48 ; 5 ; n m for background colors.

The coordinates are 1-based, origin is top left. The cursor can move within the entire screen, or in the active Scrolling Region if Origin Mode is enabled.

After writing a character, the cursor advances to the right. If it has reached the end of the row, it stays on the same line, but writing the next character makes it jump to the start of the next line first, scrolling up if needed. If Auto-wrap mode is disabled, the cursor never wraps or scrolls the screen.

Legend: Italic letters such as n are ASCII numbers that serve as arguments, separated with a semicolon. If an argument is left out, it's treated as 0 or 1, depending on what makes sense for the command.

Movement

Code	Meaning
\e[nA \e[nB \e[nC \e[nD	Move cursor up (A), down (B), right (C), left (D)
\e[nF \e[nE	Go n lines up (F) or down (E), start of line
\e[rd \e[cG \e[r;cH	Go to absolute position - row (d), column (G), or both (H). Use \e[H to go to 1,1.
\e[6n	Query cursor position. Sent back as \e[r;cR.

Save / restore

Code	Meaning
\e[s \e[u	Save (s) or restore (u) cursor position
\e7 \e8	Save (7) or restore (8) cursor position and attributes

Scrolling Region

Code	Meaning
\e[a;br	Set scrolling region to rows a through b and go to 1,1. By default, the scrolling region spans the entire screen height. The cursor can leave the region using absolute position commands, unless Origin Mode (see below) is active.
\e[?6h \e[?6l	Enable (h) or disable (l) Origin Mode and go to 1,1. In Origin Mode, all coordinates are relative to the Scrolling Region and the cursor can't leave the region.
\e[nS \e[nT	Move contents of the Scrolling Region up (S) or down (T), pad with empty lines of the current background color. This is similar to what happens when AutoWrap is enabled and some text is printed at the very end of the screen.

Tab stops

Code	Meaning
\eH	Set tab stop at the current column. There are, by default, tabs every 8 columns.
\e[nI \e[nZ	Advance (I) or go back (Z) n tab stops or end/start of line. ASCII TAB (9) is equivalent to \e[1I
\e[0g \e[3g	Clear tab stop at the current column (0), or all columns (3).

Other options

Code	Meaning
\e[?7h \e[?7l	Enable (h) or disable (l) cursor auto-wrap and screen auto-scroll
\e[?12h \e[?12l	Toggle cursor blinking (h on, l off)
\e[?25h \e[?25l	Show (h) or hide (l) the cursor
\e[?45h \e[?45l	Enable (h) or disable (l) reverse wrap-around (when using "move left" or backspace)

Legend: Italic letters such as n are ASCII numbers that serve as arguments, separated with a semicolon. If an argument is left out, it's treated as 0 or 1, depending on what makes sense for the command.

Code	Meaning
\e[mJ	Clear part of screen. m: 0 - from cursor, 1 - to cursor, 2 - all
\e[mK	Erase part of line. m: 0 - from cursor, 1 - to cursor, 2 - all
\e[nX	Erase n characters in line.
\e[nb	Repeat last printed characters n times (moving cursor and using the current style).
\e[nL \e[nM	Insert (L) or delete (M) n lines. Following lines are pulled up or pushed down.
\e[n@ \e[nP	Insert (@) or delete (P) n characters. The rest of the line is pulled left or pushed right. Characters going past the end of line are lost.

It's possible to dynamically change the screen title text and action button labels. Setting an empty label to a button makes it look disabled. The buttons send ASCII 1-5 when clicked. Those changes are not retained after restart.

Code	Meaning
\ec	Clear screen, reset attributes and cursor. This command also restores the default screen size, title, button labels and messages.
\e[8;r;ct	Set screen size to r rows and c columns (this is a command borrowed from Xterm)
\e[5n	Query device status, ESPTerm replies with \e[0n "device is OK". Can be used to check if the terminal has booted up and is ready to receive commands.
CAN (24)	This ASCII code is not a command, but is sent by ESPTerm when it becomes ready to receive commands. When this code is received on the UART, it means ESPTerm has restarted and is ready. Use this to detect spontaneous restarts which require a full screen repaint.
\e[n q	Set cursor style: eg. \e[3 q (the space is part of the command!). 0 - block (blink), 1 - default, 2 - block (steady), 3 - underline (blink), 4 - underline (steady), 5 - I-bar (blink), 6 - I-bar (steady). The default style (number 1) can be configured in Terminal Settings
\e]0;t\a	Set screen title to t (this is a standard OSC command)
\e]8x;t\a	Set label for button 1-5 (code 81-85) to t - e.g.\e]81;Yes\a sets the first button text to "Yes".
\e]9x;m\a	Set message for button 1-5 (code 91-95) to m - e.g.\e]94;\a sets the 3rd button to send "" when pressed. The message can be up to 10 bytes long.
\e]9;t\a	Show a notification with text t. This will be either a desktop notification or a pop-up balloon.
\e[?ns \e[?nr	Save (s) and restore (r) any option set using CSI ? n h. This is used by some applications to back up the original state before making changes.
\e[?800h \e[?800l	Show (h) or hide (l) the action buttons (the blue buttons under the screen).
\e[?801h \e[?801l	Show (h) or hide (l) menu/help links under the screen.
\e[?2004h \e[?2004l	Enable (h) or disable (l) Bracketed Paste mode. This mode makes any text sent using the Upload Tool be preceded by \e[200~ and terminated by \e[201~. This is useful for distinguishing keyboard input from uploads.
\e[?1049h \e[?1049l	Switch to (h) or from (l) an alternate screen. ESPTerm can't implement this fully, so the original screen content is not saved, but it will remember the cursor, screen size, terminal title, button labels and messages.
\e[12h \e[12l	Enable (h) or disable (l) Send-Receive Mode (SRM). SRM is the opposite of Local Echo, meaning \e[12h disables and \e[12l enables Local Echo.