Glossary · CNC and machine tools
Nonmodal command
Also known as: Non-modal command, One-shot command, Block-by-block command
German: Nichtmodaler Befehl
In CNC programming, a nonmodal command is a function that is effective only in the block in which it is programmed and does not change the active state of the control for the following blocks.
- CNC
- Standards
In one sentence
A nonmodal command acts only in the CNC block where it is programmed, for example a dwell, and must be repeated if needed again.
Example
G04 P2 makes the tool dwell for two seconds in that block only; the next block continues without a dwell.
How it applies
- Programming: Typical nonmodal commands are dwell, a return to the reference point or a single-block override of a work offset, depending on the control. Programmers have to repeat them wherever they are needed.
- Testing: When programs are run in single-block mode, nonmodal commands are easy to verify because their effect is limited to one block.
- Documentation: Programming manuals should mark each command as modal or nonmodal in the command reference, ideally in a dedicated column of the table. Readers who move between controls rely on this, because the same code can behave differently.
Nonmodal vs. modal command
A Modal command remains active until canceled; a nonmodal command acts once. Misreading a nonmodal command as modal (or vice versa) is a typical cause of unexpected tool movements, so programming examples should show both cases clearly.