Programming Isochronous Mode; Basics Of Programming - Siemens SIMATIC ET 200AL System Manual

Functions
5.7 Isochronous mode
Setting the delay time
The delay time is the time between the start of the send clock and the start of the
isochronous mode interrupt OB. STEP 7 sets the delay time automatically to the start of the
execution window by default. As a result, the isochronous mode update of the process image
partition automatically falls within the execution window of the application cycle.
You can also set the delay time manually. A shorter delay time enables you to increase the
processing time for your user program in the isochronous mode interrupt OB. If a manual
setting is made, note that you must call the "SYNC_PI" and "SYNC_PO" instructions in the
execution window of the application cycle.
To set the delay time for your isochronous mode application, follow these steps:
1. Open the "Properties" dialog of the isochronous mode interrupt OB under consideration.
2. In the area navigation, click the "Isochronous mode" group .
3. Clear the "Automatic setting" check box.
4. Enter your desired delay time in "Delay time (ms)".
Figure 5-75
5.7.5

Programming isochronous mode

5.7.5.1

Basics of Programming

Programming in the isochronous mode interrupt OBs
You program the isochronous section of the program exclusively in the isochronous mode
interrupt OBs Synchronous Cycle (OB 6x).
Because the isochronous mode interrupts are processed with high priority, only the time-
critical sections of the program should be processed in the isochronous mode interrupt OB.
The isochronous mode interrupt OB is called with a configured delay time.
226
Setting the delay time
PROFINET with STEP 7
Function Manual, 05/2021, A5E03444486-AL