Code availability

A new remap needs an unallocated code. The tables below match the LinuxCNC interpreter shipped by Ctrl. Do not use a listed code for unrelated behavior.

Ctrl-reserved M-codes

Ctrl reserves these codes across all machine types:

Code	Reserved meaning
`M10`	Unclamp workholding
`M11`	Clamp workholding
`M14 P<device> Q<mode>`	Select workholding grip: Q0 external (OD), Q1 internal (ID)
`M16 P<gear>`	Select the specified spindle gear
`M20`	Retract or release the tailstock quill
`M21`	Extend or engage the tailstock quill

A machine without the corresponding mechanism may leave the code unconfigured, but must not give it another meaning.

See Automatic workholding, Spindle gearbox, and Tailstock quill for the complete peripheral contracts.

Occupied LinuxCNC G-codes

Range	Occupied codes
`G0-G9.9`	`G0`, `G1`, `G2`, `G3`, `G4`, `G5`, `G5.1`, `G5.2`, `G5.3`, `G6`, `G6.1`, `G6.2`, `G6.3`, `G7`, `G8`
`G10-G19.9`	`G10`, `G17`, `G17.1`, `G18`, `G18.1`, `G19`, `G19.1`
`G20-G29.9`	`G20`, `G21`, `G28`, `G28.1`
`G30-G39.9`	`G30`, `G30.1`, `G33`, `G33.1`, `G38.2`, `G38.3`, `G38.4`, `G38.5`
`G40-G49.9`	`G40`, `G41`, `G41.1`, `G42`, `G42.1`, `G43`, `G43.1`, `G43.2`, `G49`
`G50-G59.9`	`G52`, `G53`, `G54`, `G55`, `G56`, `G57`, `G58`, `G59`, `G59.1`, `G59.2`, `G59.3`
`G60-G69.9`	`G61`, `G61.1`, `G64`
`G70-G79.9`	`G70`, `G71`, `G71.1`, `G71.2`, `G72`, `G72.1`, `G72.2`, `G73`, `G74`, `G76`
`G80-G89.9`	`G80`, `G81`, `G82`, `G83`, `G84`, `G85`, `G86`, `G87`, `G88`, `G89`
`G90-G99.9`	`G90`, `G90.1`, `G91`, `G91.1`, `G92`, `G92.1`, `G92.2`, `G92.3`, `G93`, `G94`, `G95`, `G96`, `G97`, `G98`, `G99`

Blank code points are candidates for a G-code remap. LinuxCNC accepts new G-code remaps only in modal group 1.

Occupied or reserved M-codes

Range	Occupied codes
`M0-M9`	`M0`, `M1`, `M2`, `M3`, `M4`, `M5`, `M6`, `M7`, `M8`, `M9`
`M10-M19`	`M10`, `M11`, `M14`, `M16`, `M19` (`M10`, `M11`, `M14`, and `M16` are reserved by Ctrl)
`M20-M29`	`M20`, `M21` (reserved by Ctrl)
`M30-M39`	`M30`
`M40-M49`	`M48`, `M49`
`M50-M59`	`M50`, `M51`, `M52`, `M53`
`M60-M69`	`M60`, `M61`, `M62`, `M63`, `M64`, `M65`, `M66`, `M67`, `M68`
`M70-M79`	`M70`, `M71`, `M72`, `M73`
`M80-M89`	None
`M90-M99`	`M99`
`M100-M199`	Conventional user-defined M-code range; do not remap it with `REMAP`.

M200-M999 are available for remapping. The examples use M400 and M401 from this range so they do not replace a built-in or Ctrl-reserved command.

Ctrl’s LinuxCNC build permits explicit redefinition of T, S, F, M0, M1, M6-M9, and M60-M68. Redefining one replaces its built-in interpreter behavior. Consult the LinuxCNC remap manual before doing so.