Siemens SIMATIC ET 200M Operating Instructions Manual page 167

Overlapping of Ti and To
A reduction of the system reaction time is attained with the overlapping of Ti and To,
meaning that the time from the occurence and detection of an event via the processing up to
outputting of a reaction at the outputs is reduced.
This function is only possible with the IM 153-2BAx1 interface modules. Hence these
interface modules are capable (with cycle times ≥ 0.5 ms) of supplying data isochronically to
the I/O modules via the PROFIBUS DP or of collecting data from the I/O modules.
Requirements
The following requirements must be fulfilled:
• For equidistance cycle ≥ 0.625 ms:
– Interface module IM 153-2; order number 6ES7153-2BA00-0XB0 as of E01
– as of STEP 7 V5.2 or GSD rev. 4
• For equidistance cycle ≥ 0,5 ms:
– Interface module IM 153-2; order number 6ES7153-2BAx1-0XB0 as of E01
– as of STEP 7 V5.4 or GSD rev. 5
• The transmission rate of the PROFIBUS DP is at least 1.5 Mbps (shorter equidistance times
can be achieved with higher transmission rates).
• The maximum equidistance cycle is 32 ms.
• The equidistant master must be a DP master of class 1, i.e. a PD / PC cannot be an
equidistant master.
• In equidistant mode only one DP master (class 1) can be active on the PROFIBUS DP.
Programming devices or PCs (Class 2) can also be connected.
• The isochrone mode can only be activated on the ET 200M if the equidistant bus cycle is
enabled on the DP master system and at least one module has been configured with
synchronization support.
If the ET 200M is being run on a non-S7 DP master, a stable equidistant operation is then only
ensured if the DP master fulfils the following requirements:
• The DP master must be configured with interrupt mode "delayed".
This way the data transfer is not interrupted. A diagnostic frame is inserted into the next
free time window for acyclic jobs.
• The DP master must be working with the repeat strategy "retry next cycle".
The repetition of a message frame therefore does not take place in the same cycle in
which the fault occurred, but in the cycle following.
• The DP master must support the modified target rotation time procedure (in acc. with
IEC 61784-1:2002 Ed1 CP 3/1) for further active subscribers.
Otherwise, asynchronous events (such as process interrupts, diagnoses) can cause cycle
failures or larger jitters. You can usually assume such failures / greater jitters will occur if
asynchronous events occur very frequently.
ET 200M
Operating Instructions, 04/2022, EWA-4NEB7806006-09
Functions
8.6 Isochrone mode
167