Commands starting with $ are not G-code but instructions to Grbl itself. You type them into the command line in the machine window (Console tab). Most of them only work while the machine is idle.
$$ · Show settings
Lists all settings with number and value. The app reads them itself when connecting.
$x=Wert · Change a setting
Writes a value permanently into the controller, for example $110=3000. Only possible while idle.
Example:
$110=3000$# · Show offsets
Shows the stored zeros G54 to G59, G28, G30, G92, the tool length and the last probe result.
$G · Active modes
Shows which modes are active, for example [GC:G0 G54 G17 G21 G90 G94 M5 M9 T0 F0 S0].
$I · Build info
Shows version and options of the firmware. The app uses it to recognise Grbl, grblHAL or FluidNC.
$N · Startup lines
Shows two lines Grbl runs after every start. Set with $N0=…, for example $N0=G21 G90.
$C · Check mode
Toggles check mode: Grbl reads the lines but moves nothing. That way you find errors in G-code without risk.
$X · Unlock
Clears the alarm lock without homing. Afterwards the position is not verified; after limit alarms better use $H. In the app: Unlock button.
$H · Homing
Moves to the limit switches and thereby learns the exact position. Needs $22=1. In the app: Homing button, more in Homing.
$J= · Jog
Motion command for manual moves. It can be stopped any time with the jog-cancel real-time command and changes no modes. The app uses it for the jog pad, continuous jogging and the phone.
Example:
$J=G91 X10 F1000$RST=$ · Reset settings
Resets all $ settings to the firmware defaults. Careful: afterwards steps/mm and travel usually no longer match the machine.
$RST=# · Clear offsets
Clears all stored zeros (G54 to G59, G28, G30).
$RST=* · Reset everything
Resets settings, offsets and startup lines. Only use it if you have noted the machine's values.
$SLP · Sleep
Switches spindle, coolant and motors off and waits for a reset.