# LinuxCNC M63 Digital Output Off, Synchronized

Instructions · `M63` · verification: source checked

M63 turns a digital output off, with the change queued to occur in step with machine motion. The P word selects the output number, which ranges from 0 to a default maximum of 3. The queued change is applied at the start of the next motion command, so a motion G-code should follow the M63.

## Specification

| Property | Value |
|---|---|
| Language | gcode |
| Code | M63 |
| Group | digital output control |
| Syntax | M63 P- |
| Dialect | LinuxCNC |

### Parameters

| Name | Description |
|---|---|
| P- | Digital output number, ranging from 0 to a default value of 3; adjustable using the num_dio parameter when loading the motion controller. |

## Study notes

- M63 belongs to the M62-M65 digital output control group; M62 turns an output on synchronized with motion, and M64/M65 turn an output on/off immediately.
- The P word specifies the digital output number and ranges from 0 to a default value of 3; the count can be increased with the num_dio parameter when loading the motion controller.
- M62 and M63 commands are queued; a later command referring to the same output number overwrites the earlier setting, and multiple output changes can be programmed with more than one M62/M63 line.
- The output change occurs at the beginning of the next motion command; if no motion command follows, the queued change does not happen, so a motion G-code (G0, G1, etc.) should be programmed right after M62/M63.
- M63 will not function unless the corresponding motion.digital-out-nn HAL pins are connected to outputs in the HAL file.
- M64 and M65 take effect immediately as received by the motion controller, are not synchronized with movement, and will break blending.

## Sources

1. [M-Codes](https://linuxcnc.org/docs/html/gcode/m-code.html#mcode:m62-m65) (accessed 2026-10-26)

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Source page: https://machineschema.com/instruction/mcode-m63  
JSON: https://machineschema.com/instruction/mcode-m63.json  
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite Machine Schema and the original sources.