Siemens SIMATIC ET 200AL, System Manual

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Functions
5.3 SYNC/FREEZE groups
PROFIBUS with STEP 7 V13
76
Function Manual, 12/2014, A5E03775446-AC
Important information on the control commands SYNC and FREEZE
You can use the control commands SYNC and FREEZE in the DP master to synchronize the
DP slaves event-controlled. The DP master sends the control commands simultaneously to a
group of DP slaves in its master system. It does not take into consideration DP slaves that
have failed or are currently sending diagnostic information.
Requirement for synchronization using control commands is that you have assigned the DP
slaves to SYNC/FREEZE groups.
For a S7 CPU use the instruction DPSYC_FR (SFC 11) to synchronize the DP slaves.
When you select the DP master, you see a list of the eight SYNC/FREEZE groups under
"Properties > DP interface > SYNC/FREEZE" in the Inspector window.
Figure 5-11 SYNC/FREEZE groups on DP master
SYNC control command
The DP master uses the SYNC control command to cause a group of DP slaves to freeze
the states of their outputs to the current value.
The DP slaves save the output data of the DP master for the following frames. But the states
of the DP slave outputs remain unchanged.
Only after each new SYNC control command does the DP slave set its outputs to the values
that it has saved as the output data of the DP master.
The outputs are not updated cyclically again until the DP master has sent a UNSYNC control
command.