Sync/Freeze Commands; Configuring Versions Of Sync/Freeze - Siemens SIMATIC FM 458-1 DP User Manual

4.4.4 SYNC/FREEZE commands

General
Consistency
SYNC
FREEZE
4.4.4.1

Configuring versions of SYNC/FREEZE

General
Terminology
Application Module FM 458-1 DP - User Manual
A5E01078222-02 Edition 03.2009
The SYNC and FREEZE commands synchronize the inputs and outputs
of a group of slaves. The SYNPRO function block initiates these
commands and supports the consistency checking process.
The configuring engineer is responsible in guaranteeing that data is
consistent. For the SYNC/FREEZE command, this involves consistency
of data via all of the slaves involved. It goes without saying that the
consistency of the input or output data of a slave is always guaranteed.
After initiating a SYNC command, the DP master waits for one DP bus
circulating time, so that all of the slaves have received the new output
values. The DP master then sends a SYNC broadcast telegram to the
configured slave group. All slaves of this group then simultaneously
update their buffered outputs.
The outputs are only cyclically re-updated if the DP master sends the
UNSYNC control command (EN=0 at block SYNPRO).
Ensuring consistency:
When configuring the system, it must be ensured that during a DP bus
circulating time, after the SYNC command has been initiated, output data
is not changed.
After initiating a FREEZE command, the DP master immediately
transmits a FREEZE broadcast telegram to the configured slave group.
All of the slaves of this group then simultaneously read their inputs and
buffer them. This input data is then available for the SIMADYN D CPUs
after a DP bus circulating time has expired.
Input data is only transferred again cyclically from the DP slave to the DP
master if the DP master sends the control command UNFREEZE (EN=0
at block SYNPRO).
Ensuring data consistency:
By suitably configuring, it should be ensured that during a DP bus
circulating time, after the FREEZE command has been initiated, that the
input data are not evaluated by the DP master.
The terminology involved with securing data consistency are explained
and various configuring versions of SYNC/FREEZE are illustrated.

Bus circulating time
Cycle, in which the DP master addresses all of the slaves once. In
multi-master systems, all of the masters poll their slaves. The bus
circulating time is configured and computed as a result of the baud
rate, number and type of slaves in STEP 7.
Configuring
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