• 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.
• 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 and strains the processor.
• 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. On this page, we'll use \e to indicate ESC.

Escape sequences can be divided based on their first character and structure. Most common types are:

• CSI commands: \e[ followed by 1 optional leading character, multiple numbers divided by semicolons, and one or two trailing characters. Those control the cursor, set attributes and manipulate screen content. E.g. \e[?7;10h, \e[2J
• SGR commands: CSI terminated by m. Those set text attributes and colors. E.g. \e[
• OSC commands: \e] followed by any number of UTF-8 characters (ESPTerm supports up to 64) terminated by \e\\ (ESC and backslash) or Bell (7). Those are used to exchange text strings.
• There are a few other commands that don't follow this pattern, such as \e7 or \e#8, mostly for historical reasons.

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.

All text attributes are set using SGR commands like \e[10;20;30m, 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
Blink	5	25
Inverse	7	27
Striked	9	29
𝔉𝔯𝔞𝔨𝔱𝔲𝔯	20	23

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. Here are some examples:

Key	Code	Key	Code
🡑	\e[A	F1	\eOP
🡓	\e[B	F2	\eOQ
🡒	\e[C	F3	\eOR
🡐	\e[D	F4	\eOS
Home	\eOH	F5	\e[15~
End	\eOF	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	CR (13)	F11	\e[23~
Ctrl+Enter	LF (10)	F12	\e[24~
Tab	TAB (9)	ESC	ESC (27)
Backspace	BS (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 in the current version does not implement standard mouse input. Instead, clicks/taps produce CSI sequences \e[r;cM (row, column). You can use this for virtual on-screen buttons.

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.

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[?25h \e[?25l	Show (h) or hide (l) the cursor

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[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.

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 fully supports UTF-8, you can probably ignore this feature and use Unicode directly. It's added for compatibility with some programs that use this.

The following codepages are implemented:

• 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)

To see what character maps to which symbol, look in the source code or try it. All codepages use codes 32-127, 32 being space.

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). 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

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
\e]0;title\a	Set screen title (this is a standard OSC command)
\e]81;btn1\a \e]82;btn2\a \e]83;btn3\a \e]84;btn4\a \e]85;btn5\a	Set button 1-5 label - eg. \e]81;Yes\a sets the first button text to "Yes".

Code	Meaning
\ec	Clear screen, reset attributes and cursor. The screen size, title and button labels remain unchanged.
\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.