Siemens Sinumerik 840D sl Programming Manual page 36

Fundamental Principles of NC Programming
3.2 Structure and contents of an NC program
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
● Check structures
References:
Programming Manual, Job Planning; Section: "Flexible NC programming"
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 for 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.
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Note
An identifier must be unique and cannot be used for different objects.
Programming Manual, 01/2015, 6FC5398-1BP40-5BA2
Fundamentals