Functions
5.7 Isochronous mode
PROFINET with STEP 7 V15
Function Manual, 12/2017, A5E03444486-AH
203
IPO model with application cycle factor = 1
With the IPO model with application cycle factor = 1, 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.
Figure 5-68 Program execution according to the IPO model with application cycle = 1
The figure shows the IPO model with the application cycle factor = 1 from acquisition through
processing on the CPU to output of the process values. STEP 7 calculates the delay time or
you can enter it yourself (see section Setting the application cycle and delay time
(Page 208)). During this time, the read input data and the written output data is on its way on
PROFINET IO. The delay time is set as a default to the start of the execution window.
The isochronous user program in OB 6x begins with the "SYNC_PI" instruction and ends
with the "SYNC_PO" instruction.
The "SYNC_PI" and "SYNC_PO" instructions may only be processed within the execution
window. The processing of the user program must be completed within the data cycle T_DC.
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