Siemens SIMATIC ET 200AL, System Manual

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Functions
5.7 Isochronous mode
PROFINET with STEP 7
228
Function Manual, 05/2021, A5E03444486-AL
Programming according to the IPO model in the isochronous mode interrupt OB
For programming according to the IPO model:
1.
Call the SYNC_PI instruction at the start of the isochronous mode interrupt OB.
2. Then call the actual user program.
3. Call the SYNC_PO instruction at the end of the isochronous mode interrupt OB.
Table 5- 3 Programming according to the IPO model
Step Action Explanation
1 Read in (I) The SYNC_PI instruction reads in the inputs of the process image parti-
tion and provides them to the isochronous mode interrupt OB.
2 Process (P) You program the actual user program of the isochronous mode inter-
rupt OB.
3 Output (O) The SYNC_PO instruction outputs the data changed by the user pro-
gram via the process image partition.
Signal sequence in the IPO model
The following figure shows the signal sequence in the IPO model from the acquisition and the
processing in the CPU to the output of the process values:
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 5-76 Signal sequence in the IPO model
At time T
I
the process values are read in isochronously on the I/O. The processing of the data
in the IPO model is completed within one data cycle T_DC. The output data is always available
on the I/O in the next data cycle T_DC at time T
O
.
With the IPO model, there is a constant execution time from the "input terminal" to the
"output terminal" of T
I
+ T_DC + T
O
.
T
I
+ 2×T_DC + T
O
can be guaranteed for the process response time.