SliderMC communication protocol

ASCII line protocol for the SliderMC motor controller.
Master/host is the UI controller (or a PC); device is SliderMC.
Encoding is byte = ASCII character (not Unicode).

This document is the source of truth for wire format and commands.

Maintainers: After editing command tables below, regenerate the printable cheat sheet:
python tools/render_command_cheatsheet.py
Keep descriptions aligned with GROUPS in that script (see CONTRIBUTING.md).

Design stance vs GRBL

SliderMC is a named ASCII CLI (expert-friendly, UIC-friendly), not a G-code interpreter. It borrows GRBL ideas, not G-code syntax.

GRBL 1.1	SliderMC
G-code lines + `$` settings	Two-letter commands (`MT`, `SS`, `CS`); `HL` / `?` = Help
Welcome `Grbl X.Xx ['?' for help]`	Startup `# MC V1 - Slider Motion Controller - N+M axis ['?' for help]`
Realtime single characters outside the line buffer	Same: `#` status, `!` soft stop, ESC halt, `0x18` intercepted before line assembly
Status `<Idle\|MPos:…>` on `?`	`#` and verbose push share compact `#…` lines (default 10 Hz while moving). `?` is help (needs newline).
`ok` / `error:N` per line	Motion/settings silent on success; errors `!E:code message`; queries `XX:value`
`$N=` EEPROM settings	`CS` / `CG` + `mc.ini` on LittleFS

Protocol version: VP:1 (does not bump when the wire changes). Short verbs are exactly two letters (no X/Y/Z in the verb). Long names (MoveTo, Help, …) are not accepted. Axis args may be positional or named words (X/Y/Z motors 1–3, A/B/C servos; motor 4 is positional only — see Axis args).

Not adopted: full G-code interpreter, spindle/coolant realtime, jog $J=, character-count streaming.

Live channels: CS motors 1|2|3|4 (default 1) and CS servos 0..3 (default 0). Banner {motors}+{servos} axis. IA / CG axis = packed sum (1..7; Zero 4+3, Pico 4+2). CS axis is rejected. CS motors / CS servos re-inits GPIO / PIO / PWM without RB. Letters: motors X Y Z (1–3), servos A B C; motor 4 has no letter. See Live axis count, About dual movement, and config.md / pins.md.

Wire rules

Line ends with \n. \r is ignored.
One command per line, or several separated by ;.
Values may be whitespace-separated or glued to the verb (MT100 / MT 100 / MTX20Y50Z100). Multiple values are whitespace-separated or glued named words.
Backspace (0x08 / 0x7F) edits the current line when typing.
UART (115200 baud) and USB CDC share the same parser.
Debug text is USB-only — never sent on the UIC UART.
Empty line: ignored (does not stop motion). A comment-only line (/ …) is also ignored and does not reprint the banner.
# is realtime status, not a comment. A # byte is consumed immediately and never enters the line buffer. Do not paste verbose/banner lines back into the CLI.
/ line comments: from the first / to end of line is discarded (command or ; chain). / is never a value character.
? without \n does nothing (it is not GRBL status). ?\n is help, same as HL.

Terminal Mode

Terminal Mode (ST / session terminal, init from config init_terminal) is for experts who want to watch or type on the MC while a UIC (e.g. JKSlider) drives it over UART.

Feature	Behavior
Local echo	Typed characters on the active CLI are echoed when session `terminal=1`
UART command sniff	Each complete non-empty command line from the UIC UART is copied to USB only (via the debug path) before it is executed

Goal: open the MC USB serial monitor and sniff UIC→MC command traffic without a separate UART tap. Replies, verbose #… status, and errors still use the normal reply path (UART + USB). The sniff copy never loops back onto the UIC UART.

With verbose + terminal together, status lines are still printed only when they change. Use ST 0 / CS init_terminal 0 when USB noise or echo is unwanted in production.

Startup banner

After power-up the protocol task initializes, then waits for a single \n (LF) on the UIC UART or USB CDC (whichever arrives first). Every other byte received on either port before that LF is discarded (not parsed as commands).

Only after that LF does the MC send one ready line beginning with # (hash + space), distinct from status lines (#I …, #M …). The banner is mirrored to USB + UART.

The banner always starts with # MC V1 - and always ends with {motors}+{servos} axis ['?' for help].

No device name:

# MC V1 - Slider Motion Controller - 1+0 axis ['?' for help]

With config name set, that name replaces the words Slider Motion Controller (it is not added in front of them):

# MC V1 - <name> - 1+0 axis ['?' for help]

name is printable ASCII (max 31 chars), no # or control characters. Axis text is always present, including 1+0.

sequenceDiagram
  participant Host as Host_UIC_or_USB
  participant MC as SliderMC

  Note over MC: LED+WDT init, wait LF on UART or USB
  Host->>MC: "VH\\n"
  Note over Host: UIC retries VH every 100ms until banner or 5s
  MC->>Host: "# MC V1 - …\\n"
  Note over MC: GPIO LED / WS2812 switch to McState after banner
  Host->>MC: "VP\\n"
  MC->>Host: "VP:1\\n"
  Host->>MC: "SV 1\\n"

Host recommendation (UIC MC_Client): start() sends VH\n every 100 ms until a # MC V1 - line arrives. The default wait is 5 s (banner_timeout_s=5.0). On timeout it prints UNLINKED and returns False. It does not send SV or CG. JKSlider and B4Slider still start the panel UI after that. On success it requires VP:1, then sends SV 1 and reads CG. A later empty line does not reprint the banner. VH does, after the protocol loop is running, so a UIC-only reboot can re-sync.

USB-only bench: open the MC USB serial monitor and send LF (Enter). The MC LED already blinks the wait pattern (Zero WS2812 rainbows until that LF) and WDT is armed if WDT_use=1; Enter unlocks the session, prints the banner, and switches the LED to McState patterns — no UIC or UART wiring required. USB-only idle is dim purple on the WS2812. Then type normal ASCII commands ending in \n.

Hosts can treat the banner like GRBL’s welcome string: init finished, ready for commands.

Reply classes

Class	Rule	Example
Motion / set / wait success	Silent	`MT 100`, `SS 50`, `WM`, `WP 50`, `WT`, `BE`
Error	`!E:<code> <text>`	`!E:soft soft max`, `!E:timeout`
Get / Is / Version	`<SHORT>:<value>`	`IM:1`, `GS:50.00`, `VF:1.0`, `VP:1`
Config get	`CG:<key>=<value>`	`CG:init_speed=50`
Help / Pins dump	Multi-line text (no `ok`)	`?` / `HL` → two-column command table; `VG` → `PIN_*=n`; `IG` → GP / name / desc table
Verbose push / `#`	Compact `#` status	`#M 12.5 25 80 100` (1-axis), extra packed channels after `\|` (empty `\|\|` = idle 0)

State letters

Letter	Meaning
`E`	Error (DRV / EMO)
`I`	Idle
`M`	Moving (cruise)
`A`	Accelerating
`B`	Decelerating / braking
`H`	Homing
`P`	Path playback active (`PG`)
`L`	Hard-limit alarm
`D`	Disabled
`T`	Camera trigger (`CT` pulse, or one-shot listen on `PIN_CAMERA_CTRL`)

A / B replace M only during normal-move ramps (including mid-move speed changes). Homing stays H; cruise stays M. T overlays the motion letter: while a CT pulse is active (and on verbose push if SV is on); listen is one-shot per falling edge. Verbose off → CT does not push #T (realtime # still shows T while the pulse is down).

Realtime characters (no newline)

Char	Action
`#`	Immediate status — same compact `#…` line as verbose
`!`	Soft stop (same urgency as `MS`; does not cancel waits/chain)
`ESC` (`0x1B`)	Halt (same urgency as `ME`: STEP abort, EN off, cancel waits/chain)
`0x18` (Ctrl-X)	Soft reset / clear alarm

~ (resume after hold) is reserved. Outgoing verbose/banner lines also start with #; that is TX only.

Units

API values use mm, mm/s, and mm/s² unless a config key says otherwise. Internally the controller uses steps.

Session vs config

S-commands change session RAM only (not written to mc.ini), except SD which sets live init_debug_level (USB debug; not a session field).
Power-up (and FS load) copies config init (init_speed, init_accel, init_terminal, init_verbose) into the session. init_accel seeds both live accel and decel.
Bare bool setters (SE, ST, SV, EO1…EO4): toggle the current logical state.
Bare non-bool S-commands (e.g. SS, SA, SD) reload that parameter from config init (SD → default debug level; bare SA reloads init_accel into both ramps).
SS / SA reject values above max_speed_1 / max_accel_1 with !E:limit … (session unchanged). Both SA args are checked.
CS / CG read/write persistent config keys; CS also updates the live session for keys that have a session counterpart (init_speed, init_accel, init_terminal, init_verbose).

Commands

Printable one-page overview: command-cheatsheet.html / command-cheatsheet.pdf. Markdown with Call/Reply columns: command-cheatsheet.md (regenerate with python tools/render_command_cheatsheet.py).

Descriptions below match the printable cheat sheet (tools/render_command_cheatsheet.py). Extra notes follow each group. Help (? / HL) is two columns: short + phrase.

Axis args (positional or XYZ)

Axis values for the packed live channels (STEP/DIR motors first, then RC servos; up to seven). Used by MT, MB, MJ, SP, SL, SR, PD. A line is either positional or named — never mixed (MT 20 C100 → !E:parse).

Positional: one number per channel in order, spaces between them. _ skips a slot and leaves that channel unchanged (MT _ _ 100 moves only channel 3). Omitted trailing slots are unchanged (MT 50 is channel 1 only). Motor 4 is the 4th positional field (MT 100 50 25 12.5).
Named: letters X Y Z = motors 1–3, A B C = servos 1–3, then the value (spaces optional: C100, C 100, MT C100 B50). Motor 4 has no letter. Duplicate letter, unknown letter, or a channel that is not fitted → !E:parse.
PD uses the same forms in µm (<axv_um>); skip _ or omit named → 0.
MJ uses signed percent (not mm); omitted named extra = 0; _ is invalid.
SL/SR: none clears that side (SL Z none, glued SLnone / SLZnone).
A huge MT target outside the window is rejected (!E:soft). It does not clip. Hold-to-jog uses MJ ±100 then MS. To run to a rail, MT the known window end (GR / GL).

S — Set (session, silent)

Short	Phrase	Args	Description
`SS`	Set Speed	`v` or bare	Cruise speed mm/s (≤ `max_speed_1`); bare reloads `init_speed`; applies live to the next fill (including joy-mode `MJ`).
`SA`	Set Accel	`a [d]` or bare	Accel mm/s², optional decel mm/s² (both ≤ `max_accel_1`). One value sets both ramps; two values split start vs stop. No skip `_`. Bare reloads `init_accel` into both. Applies live to the next fill (including joy-mode `MJ`).
`SE`	Set Enable	`0\|1` or bare	Driver enable 0\|1; bare toggles; required before motion; off stops hard. `SE 0` also stops servo PWM (limp); `SE 1` restores the last pulse.
`ST`	Set Terminal	`0\|1` or bare	Terminal Mode 0\|1; bare toggles; local echo + UART command sniff to USB.
`SV`	Set Verbose	`0\|1` or bare	Verbose status push 0\|1; bare toggles. While moving, default 10 Hz (`verbose_rate_hz`). Idle/disabled with terminal off is change-triggered plus a 1 s heartbeat.
`SD`	Set Debug	`0..5` or bare	USB-only debug level 0..5; bare restores default; never sent on UIC UART.
`SL`	Set Left	axis args or bare	Session working-window min; bare → envelope (`MOTOR_`/`SERVO_` / packed `axis_min_N`); `none` clears that side (effective → envelope if set).
`SR`	Set Right	axis args or bare	Session working-window max; bare → envelope; `none` clears that side.
`SP`	Set Position	axis args or bare	Redefine the reported pose (no motion). Idle only. Bare or `SP 0` = here is zero.

SetMaxSpeed / max accel / envelope soft travel are not session commands — use CS max_speed_1 / CS max_accel_1 / CS MOTOR_N_min / CS MOTOR_N_max / CS SERVO_N_min / CS SERVO_N_max (packed write-through axis_min_N / axis_max_N). CS slider_* is rejected. The live working window is SL / SR — working-window.md. SP is the origin tool when home_mode_N=0 (and is allowed after power-up even if homing is 1–4).

G — Get (session)

Short	Phrase	Args	Description
`GS`	Get Speed	—	Reply `GS:<mm/s>` — current session cruise speed.
`GA`	Get Accel	—	Reply `GA:<accel> <decel>` — current session accel and decel (mm/s²). After `SA 200`, `GA:200.00 200.00`.
`GE`	Get Enable	—	Reply `GE:0\|1` — driver enable state.
`GT`	Get Terminal	—	Reply `GT:0\|1` — Terminal Mode state.
`GV`	Get Verbose	—	Reply `GV:0\|1` — verbose push state.
`GD`	Get Debug	—	Reply `GD:<0..5>` — USB debug level.
`GL`	Get Left	—	Reply effective left as pipe groups (`GL:0 \| -45`); session None + envelope set → envelope; both None → `-`. Idle 0 is kept explicit.
`GR`	Get Right	—	Reply effective right (same pipe / `-` rules as `GL`).

I — Is / Info

Short	Phrase	Args	Description
`IM`	Is Moving	—	Reply `IM:0\|1` — axis currently moving (or settling).
`IH`	Is Homing	—	Reply `IH:0\|1` — homing cycle active.
`IL`	Is Limit	—	Reply `IL:0\|1` — at soft-limit position.
`IE`	Is Error	—	Reply `IE:0\|1` — `PIN_DRV_ERROR` / EMO latched.
`IP`	Is Position	—	Reply `IP:` packed `
`IA`	Is Axis	—	Reply `IA:<n>` — packed live count = `motors+servos` (`CG axis` is the same sum).
`IT`	Is Target	—	Reply `IT:<mm>\|-` — axis-1 seek target, or `-` if none.
`IR`	Is Ready	—	Reply `IR:1` only if idle, not homing, enabled, and not waiting.
`IW`	Is Waiting	—	Reply `IW:1` if any `WT` / `WM` / `WH` / `WP` / `WC` / `WN` wait is active.
`ID`	Is Diag	—	Reply four per-motor underrun counts, peak STEP Hz, overshoot steps, four per-motor min FIFO levels (`underrun=u0,u1,u2,u3 … fifo_min=f0,f1,f2,f3`).
`IC`	Is Cause	—	Reply last chip reset cause (`power\|wdt\|run\|soft\|debug\|brownout\|…`) as `IC:…`.
`IG`	Is GPIO	—	ASCII table of GP / name / desc. Extra-axis rows only when that axis is live; `PIN_CAMERA_CTRL` always listed (`CT` / listen); `PIN_BUZZER` when `BUZZER_use=1`.

Enable state: use GE (GetEnable). There is no IsEnabled command.

M — Movement (silent)

Short	Phrase	Args	Description
`MT`	Move To	axis args	Absolute units; skip `_` or omit named axis idles that axis; needs enable; live-retargets.
`MD`	Move Duration	`ms` then axis args	Same targets as `MT`. Arrive in `ms` (1..60000). Cruise is distance/time. Does not change session `SS`. Faster than `max_speed` is `!E:speed`.
`MF`	Move For	`ms` `ramp_ms` then axis args	Same targets as `MD`. Each ramp lasts `ramp_ms`, and `2 * ramp_ms` is less than `ms`. Cruise is distance over the remaining time. Does not change session `SS`. Too fast is `!E:speed`.
`MB`	Move By	axis args	Relative units; same skip / named rules as `MT`.
`MJ`	Move Joy	axis args	Joystick velocity hold: signed % of session `SS`; omit named extra → `0`; `0` = soft-stop; `SS`/`SA` stay live; clamp to `max_speed_N`.
`MH`	Move Home	`[1\|2\|3\|4]`	Homing cycle for a motor only; optional axis `1` (default) through live `motors`; no-op if that motor `home_mode_N` is `0` (use `SP` for origin); needs `SE 1`; cancel with `MS`/`ME`. Motor 4 has no fault pin and no limits, so stall/limit home is not useful (`home_mode_4` typically `0`). Servo letters (`A`/`B`/`C`) → `!E:parse`. There is no servo homing.
`MS`	Move Stop	—	Soft decelerate to stop; keeps enable; ends joy-mode; does not cancel waits.
`ME`	Move E-Stop, Halt	—	Immediate STEP abort; enable off; cancel waits and remaining `;` chain.

There is no ML / MR jog. Hold-to-jog: SS then MJ ±100 (per-axis 0 on extras), MS on release. Run-to-rail: MT a known GL/GR end (a huge target is !E:soft, not clipped).

Skip token (exact _ only, positional): on MT/MB/SL/SR/SP leave that axis unchanged; on PD become 0 µm. none / N / * are not skips (!E:parse on MT/MB/PD). On SL/SR only, none clears that session side (see working-window.md). MJ does not accept _ (!E:parse). Bare - is not a skip. 1-arg calls stay valid.

MH failures: !E:home cfg, !E:home travel, !E:home hard, !E:home stall. Soft-cancel with MS; emergency abort with ME. home_mode_N 1/2 = LIMIT_L/R; 3/4 = stall / DRV_ERROR (EN pulse, then drive out). See config.md / motion.md.

MJ is a velocity hold for analogue sticks (typically 5–20 Hz, also acyclic). First MJ enters joy-mode; MT/MB/MH/MS/!/ME/PG end it. SS/SA do not end joy-mode — they rescale/re-ramp from the last percentages. Soft/hard rails stop like other moves (soft rail is silent; no !E spam while the stick stays deflected). It is recommended for the sender (UIC) not to send an MJ command if the value has not changed. Integrator guide: motion-joy.md.

P — Path (host-authored motion path)

A 2nd, simpler planner for a host-authored motion path: fixed-size time slices, each carrying a signed distance in µm. PG plays the buffer at a constant per-slice rate (no accel/decel ramps — the host is trusted to pre-shape speed/accel); MS/ME end path-mode and decelerate normally from the last path speed, same as a live move.

Short	Phrase	Args	Description
`PC`	Path Clear	—	Clear the path buffer (path count → 0); rejected with `!E:busy` while `PG` is active.
`PD`	Path Data	axis args	Append signed 16-bit µm sample(s) (-32768..32767); skip `_` or omit named → `0`; increments path count; `!E:parse` / `!E:full`. Allowed while `PG` is active (live-move streaming).
`PG`	Path Go	— or `start end`	Bare: play sample 0 through `path_count-1`, then soft-stop. `PG <start> <end>`: 0-based inclusive sample indices. If `start > end`, play reverse with negated deltas. Host is already at the start-index pose (before sample `start` going forward, or after sample `start` going reverse). Reject either index `< 0` or `>= path_count` (`!E:range`). Needs enable; `!E:disabled` / `!E:empty` / `!E:busy`. May be sent while `PD` is still being streamed in (live move).
`PN`	Path Number	—	Reply `PN:<count>` — number of samples currently in the buffer; allowed even while path-mode is active.
`PI`	Path Index	—	Reply `PI:<play_index>` — 0-based playhead (0 if idle). Allowed during `PG` like `PN`. Not a GPIO command.
`PS`	Path Slice	`us` or bare	Set the time-slice length in µs (≥1000); bare reloads `init_path_slice_us`; `!E:parse` below minimum, `!E:busy` while active.

A sample value of 0 means the axis stands still for that slice. Distance→steps and slice-time→PIO-cycles both use an error-diffusion accumulator so rounding never biases total distance or total playback time. steps_per_unit_N and PIO limits apply as usual; speed/accel limits are not checked — the host is expected to deliver an already speed/accel-limited path.

While PG is active, all other move/session commands are rejected with !E:busy — allowed exceptions: MS, ME, RB, PD (live-move streaming), PN, PI, EI, all I*/G*/V* queries, IG, HL/?, CG, BE, CT. The buffer is retained after playback ends (naturally or via MS/ME), so PG can replay the same data.

Verbose / # while in path-mode (state letter P) use the same layouts as other moving states (#P … with live pos/speed; accel is typically 0 for constant-rate slices).

E — Extender (silent)

Short	Phrase	Args	Description
`EO`	Ext Out	`n [0\|1]`	Channel `1`…`4` (`EO1`…`EO4`); bare toggles; `EO1 1` set on; ok during EMO. Sets level when mode is `O` or `T`; `EO` on `I` switches to push-pull `O`.
`ED`	Ext Dir	`n I\|O\|T`	Channel `0`…`3` (`ED0`…`ED3`): I input+pull-up (boot default), O push-pull output, T open-collector + pull-up. Do not use `PD`/`PI` for pins (`PD` is Path Data, `PI` is Path Index).
`EI`	Ext In	`n`	Channel `0`…`3` (`EI0`…`EI3`); reply `EI:<n> <0\|1>` (electrical HIGH=1). Works in I, O, and T. Allowed during `PG`.

EO5… is !E:parse (PIN_EXT_COUNT is 4). Levels use EXT_1_active…EXT_4_active (EO1 is extender 1, ED0/EI0 are the same pin). Reset to inactive on reboot; pin mode defaults to I. Beep / camera pulse are Special (BE, CT).

C — Config (persistent)

Short	Phrase	Args	Description
`CS`	Config Set	`key value`	Set persistent key value (`mc.ini`); silent ok; updates session init_speed/init_accel/….
`CR`	Config Reset	—	Reset all config to compiled defaults and save `mc.ini`.
`CG`	Config Get	`key` or bare	Get key → `CG:key=value`; bare dumps all keys.

Important keys: init_speed, init_accel, max_speed_1, max_accel_1, max_speed_2, max_accel_2, max_speed_3, max_accel_3, steps_per_unit_1, motor_N_unit / servo_N_unit (stored; defaults mm / deg), MOTOR_N_min/MOTOR_N_max, SERVO_N_min/SERVO_N_max, SERVO_N_min_pulse/SERVO_N_max_pulse/SERVO_N_swap, synthesized axis_min_N/axis_max_N and axis_N_unit (packed copy of the motor or servo label), motors, servos, axis (read-only sum; dump emits it), name, init_verbose, init_terminal, init_debug_level, pin keys with the digit before the suffix (DRV_STEP_1_active, SW_LIMIT_R_3_use), BUZZER_use, home_mode_1 / home_move_out_1 / home_speed_1 / home_accel_1, matching _2 / _3 keys, ramp_start_speed, stop_approach_speed (user-units/s; old ramp_start_hz / stop_approach_hz still load as hz / 320 and are not written back), dir_change_pause_s. Synonyms: steps_per_mm_N, soft_min_N / soft_max_N (aliases of packed axis_min_N). CS axis, CS axis_N_unit, and CS slider_* are rejected. See config.md.

A UIC may shrink travel with session SL / SR (working window) — not by rewriting envelopes. See working-window.md and marks vs working window.

W — Wait (silent)

Short	Phrase	Args	Description
`WT`	Wait Time	`[sec]`	Delay sec then continue `;` chain; bare → 1 s; never `!E:timeout`.
`WM`	Wait Moving	`[timeout_s]`	Pause chain until move ends; optional timeout cancels remaining chain.
`WH`	Wait Homing	`[timeout_s]`	Pause chain until homing ends; optional timeout cancels remaining chain.
`WP`	Wait Pos	`pos [timeout_s]`	Pause until the time-sync master position is reached or overstepped; idle → return immediately.
`WC`	Wait Cruise	`[timeout_s]`	Pause until status letter `M` (cruise) or idle.
`WN`	Wait Not cruise	`[timeout_s]`	Pause until status is not `M`; idle / `A` / `B` → return immediately.

Optional timeout in seconds (float): WM100, WM 100, WP 250 5, WC 10, WN 3.
No timeout arg = wait indefinitely until the condition clears (WT is always a delay).
Success: silent (no OK); ; chain continues with the following commands.
Timeout (WM / WH / WP / WC / WN): !E:timeout and cancel all following commands on that chain. Motion is not stopped by the timeout alone.
WT delay expiry: resumes the chain silently (never !E:timeout).
WP: time-sync master only (first motor with a distance, else first servo). Second number is timeout, not a second-axis pos. Moving + → done when pos >= mark; moving − → pos <= mark. Idle / ~0 velocity → return immediately. Bare WP → !E:parse. SS/SA are in the master’s units.
WC: wait until cruise (M); also completes if not moving. While already braking (B), waits until idle (or timeout).
WN: wait while cruising; already not M → return immediately.

In-move scripting (live SS/SA at waypoints, extender cues): command chains.

V — Version

Short	Phrase	Args	Description
`VA`	Version About	—	Reply `VA:` about string (name, version, author).
`VH`	Version Hello	—	Reprint the welcome banner (`# MC V1 - …`), the same bytes as the one-shot boot banner. An empty line does not reprint it. Not `VH:…`. Allowed during path and EMO. Hosts should send `VH\\n` to align after either side reboots.
`VF`	Version FW	—	Reply `VF:<version>` — firmware version.
`VP`	Version Protocol	—	Reply `VP:<n>` — protocol version (`1`). Wire may change without bumping `VP`.
`VG`	Version GPIO	—	List `PIN_*=GPIO` lines (machine-readable). Extra-axis pins only when that axis is live; `PIN_CAMERA_CTRL` always listed; `PIN_BUZZER` when `BUZZER_use=1`.

Special

Short	Phrase	Args	Description
`RB`	Reboot	—	Soft MCU reset (no power cycle); EN off first. Allowed during EMO / path. Next `IC` → `soft`.
`BE`	Beep	`[ms]`	Pulse `PIN_BUZZER` (non-blocking). Bare → 100 ms; clamp 1..1000. Not a wait (`IW` unchanged). No-op if `BUZZER_use=0` or the pin aliases `PIN_LED`. OK during EMO / path. Re-issue restarts the pulse. Enable with `CS BUZZER_use 1` (default 0).
`CT`	Camera Trigger	`[ms]`	Pulse `PIN_CAMERA_CTRL` low (open-collector sink, 12 mA), then release to pull-up. Bare → 100 ms; clamp 1..60000. Not a wait; motion continues. OK during EMO / path. Status letter `T` while pulsing (verbose on: at least one `#T`; verbose off: silent). Wiring: pins.md.
`HL` / `?`	Help	—	Two-column ASCII table of all commands. `?` needs newline (not realtime).

Realtime # / ! / ESC are not line commands — see Realtime characters. Breaking wire (ME, ? help, # status only, / comments, CT) does not bump VP — still VP:1.

Stop vs Halt

Command	Deceleration	Enable	Waits / `;` chain
`MS` / realtime `!`	Soft (accel ramp)	unchanged	not canceled (`!`); `MS` does not cancel waits
`ME` / realtime `ESC`	Immediate hard abort	forced `0`	canceled

Hard-limit trips and PIN_DRV_ERROR use the same internal halt path as ME.

`PIN_DRV_ERROR` (E-stop / driver fault)

Polled with ~20 ms debounce (including already asserted at power-up). While asserted: IE:1, state letter E, halt applied, most commands rejected with !E:emo active.

Allowed while error active: IE, IA, ID, IC, IG, VA/VF/VP/VG/VH, HL/?, CS/CR/CG, ME, RB, EO1…EO4, EI0…EI3, BE, CT, realtime # / ! / ESC / 0x18. When the pin releases, drv_error clears (enable stays 0 until SE 1).

Live axis count (`motors` + `servos`)

Board	Support
Pico / Pico W / Pico 2 / Pico 2 W	`CS motors 1..4`, `CS servos 0..3`. Servo PWM on GP26/27/18. GP18 steals EXT_4 when `servos>=3`; motor 4 DIR also claims GP18, so `motors>=4` caps servos at 2. Motor 4 STEP is GP19 (EXT_3).
RP2040-Zero / RP2350-Zero	Same motor/servo counts. Servo PWM on GP23/22/21. Motor 4 DIR/STEP is GP19/20 (EXT_3/EXT_4); servos stay. UART is GP12/13, not the Pico GP16/17 pair. Camera is GP29; LED is GP25.

Packed live channels = motors + servos (1..7; Zero 4+3, Pico 4+2). IA replies that sum; bare CG dump includes synthesized axis=<sum>. Extra-arg MT/MB/PD/MJ/SL/SR/SP apply (motors then servos). Motor 4 is STEP/DIR only (no fault, no limits). WP uses the time-sync master. IG / VG list extra motor / servo pins only while fitted; PIN_CAMERA_CTRL is always listed (CT / listen). See pins.md. Joy-mode (MJ) drives packed channels independently (not dual-MT time-sync) — motion-joy.md.

Servo PWM: 100 Hz, wrap 65535. Envelope ±135° maps onto SERVO_N_min_pulse…max_pulse (default 500–2500 µs; analog 1000–2000). Default-span resolution is ~1.25 arc minutes (′) per PWM count (~0.021°). SERVO_N_swap reverses mechanical sense; SERVO_N_active inverts polarity. SE 0 stops PWM (limp); SE 1 restores the last pulse. Boot pose 0° is clamped to the envelope. Path buffer is split across packed channels (PATH_AXES 7).

Verbose push (default 10 Hz while moving)

Verbose mode pushes compact #… status so the UIC can refresh a display (e.g. OLED). It also acts as a heartbeat that the MC is alive.

Each packed channel is a 1-axis field group. Extra live channels append the same group after a | separator. The state letter is machine-wide (one McState), not per-axis. Idle lone 0 elides; empty || groups are idle 0 (#I 10 || -45). IP / GL / GR keep explicit 0 with |.

1-axis group (`motors+servos=1`, or each side of `|`)

#<state> <pos> [<speed> <accel> [<target>]]

Homing (#H) includes speed and accel but omits target. Servos are never homed.

Extra packed channels

#<state> <pos1> [<speed1> <accel1> [<target1>]] | <pos2> … [| …]

State	Line
Idle / non-moving (`I`, `E`, `D`, `L`, …)	`#<letter> <pos1> \| <pos2>` (empty group `\|\|` = idle 0)
Homing (`H`)	`#H <pos1> <speed1> <accel1> \| <pos2> …` — no targets
Moving (`M`, `A`, `B`, `P`, …)	`#<letter> <pos1> <speed1> <accel1> <target1> \| <pos2> …`

A 1-axis reader can take the first group and ignore everything after |.
Count of | separators is packed-count − 1 when groups are not elided; trailing idle 0 may be omitted.
Numbers use at most 2 decimal digits, without trailing zeros (100, 100.1, 0.1).
When moving/homing, speed / accel magnitudes use absolute values (fabs).
accel is measured dv/dt magnitude (lightly smoothed), not the SA setpoint; 0 in cruise.
1-axis target is present only for position seeks (not continuous jog / soft-stop bleed). Multi-axis moving lines emit a target per group.
Default rate is verbose_rate_hz 10 (1..200). While moving, homing, or otherwise not idle/disabled, lines are pushed at that rate even if unchanged.
Idle or disabled, with terminal off: a line is sent when it changes, and again as a 1 s heartbeat if it has not.
Terminal Mode dedupes at verbose_rate_hz: a line is sent only when it differs from the previous one.

Examples (1 packed channel):

#I 12.5
#A 12.5 10 80 100
#M 12.5 25 0 100
#H 10 25 20
#L 0

Examples (2 packed channels):

#I 123.45 | 67.8
#H 10 25 20 | 0 25 20
#M 123.45 10 50 200 | 67.8 5 25 90

Examples (1 motor + 2 servos, idle 0 elided in the middle):

#I 10 || -45
#M 10 25 0 100 | 0 0 0 0 | -45 5 20 -45

Status report (`?`)

Same format as verbose push (one immediate #… line).

Error codes

Code	Meaning
`parse`	Unknown command or bad arguments
`disabled`	Motion while disabled
`soft`	Soft-limit rejection
`hard`	Hard-limit / alarm
`emo`	`PIN_DRV_ERROR` active / command blocked (`active`)
`busy`	Illegal during homing/alarm
`cfg`	Unknown config key or bad value
`home`	Homing rejected/aborted (`cfg`, `travel`, `hard`)
`timeout`	`WM` / `WH` / `WP` / `WC` / `WN` timed out; remainder of `;` chain canceled

Format: !E:<code> <short text>

Examples

SE 1
SS 50
SA 200
SA 200 50
MT 100;WM
IM
VA

Typical replies:

IM:0
VA:Slider Motion Controller V1.0 by Jochen Krapf

MT 500;WM 30;SS 10

If the move is not finished within 30 s → !E:timeout and SS 10 is not executed.

MT 100;WM;SS 12
ME

ME emergency-halts (EN off) and cancels the wait / following SS 12.

WT;GS

After ~1 s delay, GS runs.

SS20;MT300;WP100;SS50;WP200;SS20;WM
SA100;MT300;WC;SA5;WM
MT 500; WP 250; EO1 1; WM

In-move retarget and cues (no stop between marks): command chains.

#
#I 100

SV 1
#I 100

Joystick hold (see motion-joy.md). UIC should not resend MJ if the value is unchanged:

SE 1
SS 30
MJ 5
MJ 10
MJ 100
SS 50
MJ 100
MJ 50
MJ 0
MS

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protocol.md

protocol.md

SliderMC communication protocol

Design stance vs GRBL

Wire rules

Terminal Mode

Startup banner

Reply classes

State letters

Realtime characters (no newline)

Units

Session vs config

Commands

Axis args (positional or XYZ)

S — Set (session, silent)

G — Get (session)

I — Is / Info

M — Movement (silent)

P — Path (host-authored motion path)

E — Extender (silent)

C — Config (persistent)

W — Wait (silent)

V — Version

Special

Stop vs Halt

`PIN_DRV_ERROR` (E-stop / driver fault)

Live axis count (`motors` + `servos`)

Verbose push (default 10 Hz while moving)

1-axis group (`motors+servos=1`, or each side of `|`)

Extra packed channels

Status report (`?`)

Error codes

Examples

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protocol.md

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SliderMC communication protocol

Design stance vs GRBL

Wire rules

Terminal Mode

Startup banner

Reply classes

State letters

Realtime characters (no newline)

Units

Session vs config

Commands

Axis args (positional or XYZ)

S — Set (session, silent)

G — Get (session)

I — Is / Info

M — Movement (silent)

P — Path (host-authored motion path)

E — Extender (silent)

C — Config (persistent)

W — Wait (silent)

V — Version

Special

Stop vs Halt

PIN_DRV_ERROR (E-stop / driver fault)

Live axis count (motors + servos)

Verbose push (default 10 Hz while moving)

1-axis group (motors+servos=1, or each side of |)

Extra packed channels

Status report (?)

Error codes

Examples

`PIN_DRV_ERROR` (E-stop / driver fault)

Live axis count (`motors` + `servos`)

1-axis group (`motors+servos=1`, or each side of `|`)

Status report (`?`)