Siemens SIMATIC ET 200SP Manual page 21

Isochronous mode
The technology module supports the "isochronous mode" system function in distributed
operation. This system function enables counter values and measured values to be acquired
in a defined system cycle.
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 change in the state of a digital
input immediately affects the planned reaction of the technology module and changes the
status bit of the digital input in the feedback interface (Page 55).
Data processing
The data that was transmitted to the technology module in the current bus cycle via the
control interface takes effect when it is processed in the internal technology module cycle.
The counter value and the measured value as well as status bits are captured at time T
made available in the feedback interface for retrieval in the current bus cycle.
Additional information
A detailed description of isochronous mode can be found in the PROFINET with STEP 7
function manual, which is available for download on the Internet
(https://support.industry.siemens.com/cs/ww/en/view/49948856).
Technology Module TM Count 1x24V (6ES7138-6AA00-0BA0)
Manual, 02/2017, A5E33002339-AB
Product overview
2.2 Functions
and
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