Siemens SIMATIC S7-400 Reference Manual page 51

SYNC/FREEZE
With the SYNC control command, the DP slaves of the selected groups are
switched to the Sync mode. In other words, the DP master transfers the current
output data and instructs the DP slaves involved to freeze their outputs. With the
following output frames, the DP slaves enter the output data in an internal buffer
and the state of the outputs remains unchanged.
Following each SYNC control command, the DP slaves of the selected groups
apply the output data of their internal buffer to the outputs to the process.
The outputs are only updated cyclically again when you send the UNSYNC control
command using SFC 11 "DPSYC_FR".
With the FREEZE control command, the DP slaves involved are switched to the
Freeze mode, in other words the DP master instructs the DP slaves to freeze the
current state of the inputs. It then transfers the frozen data to the input area of the
CPU..
Following each FREEZE control command, the DP slaves freeze the state of their
inputs again.
The DP master only receives the current state of the inputs cyclically again after
you have sent the UNFREEZE control command with SFC 11 "DPSYC_FR".
Power-Up of the DP Master System
Use the following parameters to set power-up monitoring of the DP master:
• Transfer of the Parameters to Module
• "Finished" Message by Means of Modules
In other words, the DP slaves must power up and be configured by the CPU (as
DP master) in the set time.
PROFIBUS Address of the DP Master
All PROFIBUS addresses are permissible.
Automation System S7-400 CPU Specifications
A5E00165965-01
Structure of a CPU 41x
s
1-39