Siemens SIMATIC ET 200SP Manual page 74

4.4.7 Isochronous mode
The technology module supports the "Isochronous mode" system function. Counter values
can be acquired in a fixed system cycle with this system function.
In isochronous mode, the cycle of the user program, the transmission of the input signals
and processing in the technology module are synchronized. The output signals switch
immediately if the relevant comparison condition is met. A status change of a digital input
immediately triggers the specified reaction of the technology module and the change of the
status bit of the digital input in the feedback interface.
This operating mode is especially well-suited for short send clocks of the CPU starting from
125 µs, because only input data is used.
Use an OB of type "Synchronous Cycle" (e.g. OB61) in this operating mode.
Data processing
At the time the input data is read in (T
and made available in the feedback interface for retrieval in the current bus cycle.
Isochronous mode parameters
In isochronous mode, the "Filter frequency" parameter can affect the isochronous mode
parameters of the sync domain.
Because the isochronous mode parameters are not checked in RUN, overflows can occur if
you change the parameters in RUN. To prevent overflows, select the option with the largest
time required in the offline parameter assignment.
Additional information
You can find a detailed description of isochronous mode in the following:
● In the isochronous mode function manual as a download from the Internet
(https://support.industry.siemens.com/cs/ww/en/view/109755401).
● Function manual PROFINET with STEP 7 available for download on the Internet
(https://support.industry.siemens.com/cs/ww/en/view/49948856)
TM Count 1x24V (6ES7138‑6AA01‑0BA0) technology module
Manual, 07/2019, A5E33002339-AD
), the counter value and the status bits are acquired
i
Configuring/address space
4.4 Fast Mode
73