Data transfer to the PLC
7.3 Functional sequences/description of functions
3WL/3VL circuit breakers with communication capability - PROFIBUS
System Manual, 03/2011, A5E01051353-02
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Figure 7-5
Diagnostic buffer of the S7
7.3.2
SYNC and FREEZE
To coordinate the data exchange, PROFIBUS DP offers the user the control commands
SYNC (synchronization of the outputs) and FREEZE (freezing of the inputs). The SENTRON
circuit breakers VL and WL support both SYNC and FREEZE mode.
With SFC11 DPSYNC_FR, the control commands are triggered from the user program of the
S7. Not every master supports this function.
SYNC/FREEZE groups
A DP master with the relevant functionality can send the SYNC and/or FREEZE control
commands (broadcast frames) to a group of DP slaves simultaneously. For this purpose, the
DP slaves are combined into SYNC and FREEZE groups. Up to 8 groups can be formed for
a master system. However, each DP slave can only be assigned to a maximum of one
group.
SYNC
The control command SYNC enables the user to synchronize the outputs on several slaves
simultaneously. When the control command SYNC is received, the addressed DP slaves
switch the data of the last Data_Exchange frame from the DP master in their transfer buffer
to the outputs. This enables simultaneous activation (synchronization) of the output data on
several DP slaves.