HEIDENHAIN iTNC 530 User Manual page 660

16.7 Optional program-run
interruption
Application
The TNC optionally interrupts program run at blocks containing M1. If
you use M1 in the Program Run mode, the TNC does not switch off the
spindle or coolant, if necessary. Your machine tool manual provides
more information.
 Do not interrupt Program Run or Test Run at blocks
containing M1: Set the soft key to OFF
 Interrupt Program Run or Test Run at blocks
containing M1: Set the soft key to ON
M1 is not effective in the Test Run mode of operation.
660 Test Run and Program Run