Siemens SINUMERIK 840Di Function Manual page 1236

Detailed Description
2.7 Structure and functions of the basic program
Jobs from PLC to NCK:
The FCs and FBs, which are used to pass jobs to the NCK, must no longer be processed by
the PLC user program, as this could lead to incorrect checkback signals. During power-up of
the control, a job (e.g. read NCK data) must not be activated in the user program until the
NCK CPU ready signal is set.
2.7.7 Functions of the basic program called from the user program
General
In addition to the modules of the basic program, which are called at the start of OBs 1, 40
and 100, functions are also provided, which have to be called and supplied with parameters
at a suitable point in the user program.
These functions can be used, for example, to pass the following jobs from the PLC to the
NCK:
• Traversing concurrent axes (FC 18)
• Start asynchronous subprograms (ASUBs) (FC 9),
• Selecting NC programs (FB 4)
• Control of spindle (FC 18),
• Read/write variables (FB 2, FB 3).
2-42
Note
The following note will later help you to check and diagnose a function call (FCs, FBs of
basic program). These are FCs and FBs, which are controlled by a trigger signal (e.g., via
parameter Req, Start, etc.), and which supply an execution acknowledgment as an output
parameter (e.g., via parameter Done, NDR, Error, etc.). A variable compiled of other
signals, which produce the trigger for the function call should be set. Start conditions may
be reset only as a function of the states of parameters Done, NDR and Error.
This control mechanism may be positioned in front of or behind the function call. If the
mechanism is placed after the call, the output variables can be defined as local variables
(advantage: Reduction of global variables, flags, data variables and time-related
advantages over data variables).
The trigger parameter must be a global variable (e.g., flag, data variable).
In OB 100, jobs still activated by the user program (Parameter Req,
Start, etc.:= TRUE) must be set to zero at the named parameters. A POWER OFF/ON
could result in a state in which jobs are still active.
PLC Basic Program Solution Line (P3 sl)
Function Manual, 08/2005 Edition, 6FC5397-0BP10-0BA0