Siemens S7-300 Operating Instructions Manual page 44

Programming the FM 352
7.3 FB CAM_CTRL (FB 1)
Jobs
Data exchange with the module other than the control and checkback signals is handled
using jobs.
To start a job, set the corresponding trigger bit in the channel DB and provide the relevant
data for write jobs. You then call FB CAM_CTRL to execute the job.
If you use the FM 352 centrally, a read job is executed immediately. If you use the FM 352 in
a distributed system, a read job may take several cycles.
Due to the required confirmations from the module, a write job requires at least 3 calls (or
OB cycles). If you use the FM 352 in a distributed system, a write job may take more than 3
calls.
You can send several jobs at the same time, if necessary, along with control signals. With
the exception of the job for writing the function switches, the jobs are executed in the order of
the trigger bits specified in the channel DB. Once a job has been completed, the trigger bit is
canceled. The next time the block is called, the subsequent job is identified and executed.
For each job there is not only a trigger bit but also a done bit and an error bit. In their names,
instead of the ending _EN for "enable", they have the ending _D for "done" or _ERR for
"error". Done and error bits of the job should be set to 0 after they have been evaluated or
before the job is started.
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 reset to 0.
Function switches
The function switches activate and deactivate module 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.
Length measurements and edge detection must not be activated at the same time. For this
reason, FB CAM_CTRL makes sure that when one of the function switches is activated, the
other is deactivated. If you do activate both function switches at the same time (0 → 1), the
length measurement is activated.
Function switches and jobs can be used at the same time in one FB CAM_CTRL call.
As with the jobs, there are done bits with the ending _D and error bits with the ending _ERR
for the function switches.
To be able to evaluate the done and error bits, you should set these bits to 0 when you
change a function switch.
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FM 352 electronic cam controller
Operating Instructions, 05/2011, A5E01071724-03