Programming the FM 351
6-6
FM 351 Positioning Module
C79000-G7076-C351-02
Return Values
The function provides the following return values:
RET_VAL BR Description
1 1 At least one job active
0 1 No job active, no error
–1 0 Error: Data error (DATA_ERR) or
communications error (JOB_ERR) occurred
Jobs
Data exchange with the module other than the control and return signals is handled
using jobs.
To start a job, you set the corresponding trigger bit in the channel DB and provide
the relevant data for write jobs. You then call FC ABS_CTRL to execute the job.
If you use the FM 351 centrally, a read job takes exactly one cycle. If you use the
FM 351 decentrally, a read job may take several cycles.
Due to the required confirmations from the module, a write job requires at least
three calls (or OB cycles).
Once a job has been executed completely, the block resets the trigger bit. The next
time the block is called, the next job is located and executed.
For each job, there is a trigger bit (extension _EN for “enable”) and a done bit and
error bit. These have the extensions _D (for “done”) or _ERR (for “error”) in the
name. FC ABS_CTRL updates the done and error bits when the job has been
executed. These bits should be set to 0 after they have been evaluated or before a
new job is sent.
If you set the JOBRESET bit, all the done and error bits are reset before the
pending jobs are processed. The JOBRESET bit is then set to 0 again.
Function Switches
The function switches activate and deactivate channel states. A job for writing the
function switches is only executed when there is a change in a switch setting. The
setting of the function switch is latched after the job has been executed.
Function switches and jobs can be used at the same time in one FC ABS_CTRL
call.
As with the jobs, the function switches have trigger bits with the name extension
_ON/_OFF, done bits with the extension _D and error bits with the extension
_ERR.
To allow evaluation of the done and error bits of the function switches, you should
set these bits to 0 before you send a job to modify a function switch.
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