Siemens SIMATIC ET 200M Operating Instructions Manual page 133

Marginal conditions
The precision of the time stamping is influenced by the following marginal conditions:
● The number of time-stamped input signals in an ET 200M influences the precision of the
● Process interrupts as well as reading / writing data records reduce the precision of the
● In the case of synchronous operation, the precision of the time stamping always
Operating principle
The IM 153-2 provides changed input signals with the respective current time and saves this
in a buffer (message list). Such a message list is a data record with maximum 20 messages
about time-stamped signal changes. Up to 15 data records can be saved in the IM 153-2.
A signal message provides the following information:
● Slot number of the (reported) DI module (4 ... 11)
● Channel number of the DI module
● Signal status (incoming, outgoing)
● Time of the signal change
When there are time-stamped signals or a data record is full, the IM 153-2 generates a
process interrupt to the DP master. The buffer is evaluated with "read data record".
In the case of events that influence the time stamping (STOP of the time stamping, time
message frame failure, ...) special messages are generated.
A special message provides the following information:
● Slot number of the IM 153-2 (always "2")
● Code of the special message (e.g. STOP of the time stamping)
● Characteristic of the special message (e.g. incoming / outgoing)
● Time of the special message
ET 200M
Operating Instructions, 12/2008, EWA-4NEB780600602-08
time stamping, e.g. more time-stamped input signals reduce the precision of the time
stamping.
time stamping.
The specified precisions for time stamping (10 ms or 1 ms) will however remain.
corresponds to the DP cycle time.
8.2 Time stamping the input signals with IM 153-2
Functions
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