Siemens SINUMERIK 840D sl Programming Manual page 45

These include, for example:
● Commands of the NC high-level language
In contrast to the commands according to DIN 66025, the commands of the NC high-level
language consist of several address letters, e.g.
– OVR for speed override
– SPOS for spindle positioning
● Identifiers (defined names) for:
– System variables
– User-defined variables
– Subprograms
– Keywords
– Jump markers
– Macros
● Comparison operators
● Logic operators
● Arithmetic functions
● Control structures
Effectiveness of commands
Commands are either modal or non-modal:
● Modal
Modal commands retain their validity with the programmed value (in all following blocks)
until:
– A new value is programmed under the same command.
– A command is programmed that revokes the effect of the previously valid command
● Non-modal
Non-modal commands only apply to the block in which they were programmed.
End of program
The last block in the execution sequence contains a special word for the end of program: M2,
M17 or M30.
NC programming
Programming Manual, 12/2019, 6FC5398-2EP40-0BA0
Note
An identifier must be unique and cannot be used for different objects.
2.2 Fundamental Principles of NC Programming
Fundamentals
45