Siemens SIMATIC ET 200AL, System Manual

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Functions
5.7 Isochronous mode
PROFINET with STEP 7
230
Function Manual, 05/2021, A5E03444486-AL
Signal sequence in the OIP model
The following figure shows the signal sequence in the OIP model from the acquisition of
process values and the processing in the CPU to the output of the process values. The
application cycle is twice as long as data cycle T_DC in this example.
① Execution of isochronous mode interrupt OB
② "SYNC_PI" instruction
③ "SYNC_PO" instruction
④ Isochronous read-in of process values on I/O module at time T
I
⑤ Isochronous output of process values on I/O module at time T
O
Figure 5-77 Signal sequence in the OIP model
At time T
I
the process values are read in isochronously on the I/O. The data is processed over
2 application cycles in the OIP model. The output data is always available on the I/O in the
following application cycle at time T_DC + T
O
.
With the IPO model, there is a constant execution time from the "input terminal" to the
"output terminal" of T
I
+ application cycle + T_DC + T
O
.
T
I
+ 2 x application cycle + T_DC + T
O
can be ensured as the process response time.