Isochronous Mode - Siemens SIMATIC ST-1500 Function Manual

The basics of counting, measurement and position detection
2.3 Basics of counting (TM Timer DIDQ)
2.3.5

Isochronous mode

The TM Timer DIDQ supports the "Isochronous mode" system function in decentralized
operation. This system function enables counter values to be acquired in a defined system
cycle.
In isochronous mode, the cycle of the user program, the transmission of the input and output
data and the processing in the module are synchronized with each other.
Data processing
The data that was transmitted to the module in the current bus cycle via the control interface
takes effect when it is processed in the module's internal cycle. The counter value and status
bits are detected at time T
current bus cycle.
Additional information
For a detailed description of isochronous mode, refer to the PROFINET with STEP 7 function
manual, which is available as download at Internet
(https://support.industry.siemens.com/cs/ww/en/view/49948856).
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and made available in the feedback interface for retrieval in the
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Counting, measurement and position detection
Function Manual, 12/2017, A5E32009889-AG