Siemens SIMATIC FM 452, Руководство пользователя, Страница: 44 / 210

Programming the FM 452
6-6
FM 452 Electronic Cam Controller
C79000-G7076-C452-04
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 CAM_CTRL to execute the job.
A read job is executed immediately. Due to the required confirmations from the
module, a write job requires at least three calls (or OB cycles).
You can send several jobs at the same time, if necessary, along with control
signals. Apart from the job for writing the function switch, the jobs are executed in
the order of the trigger bits as specified in the channel DB. Once a job has been
completed, the trigger bit is reset. The next time the block is called, the next job is
located 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 set to 0 again.
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. It is
always executed between the jobs “set reference point” (REFPT_EN) and “set
actual value” (AVAL_EN). 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.
FC CAM_CTRL makes sure that when one of the function switches is activated,
the other is deactivated. If you do switch 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 FC 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.
Startup
When the module or CPU starts up, call FC CAM_INIT (see Section 6.2,
Page 6-4). Among other things, the function switches are reset.
FC CAM_CTRL acknowledges the module startup. During this time, RET_VAL and
JOBBUSY are set to 1.