HEIDENHAIN TNC 410 ISO Programming User Manual
Page 177

HEIDENHAIN TNC 410, TNC 426, TNC 430
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Effect
M91 and M92 are effective only in the blocks in which they are 
programmed.
M91 and M92 take effect at the start of block.
Workpiece datum
If you want the coordinates to always be referenced to the machine 
datum, you can inhibit datum setting for one or more axes; (see 
“General User Parameters” on page 422). 
If datum setting is inhibited for all axes, the TNC no longer displays the 
soft key DATUM SET in the Manual Operation mode.
The figure at right shows coordinate systems with the machine datum 
and workpiece datum.
M91/M92 in the Test Run mode
In order to be able to graphically simulate M91/M92 movements, you 
need to activate working space monitoring and display the workpiece 
blank referenced to the set datum, see “Showing the Workpiece in 
the Working Space (not TNC 410),” page 408.
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