Technical data

SFCs for Distributed I/Os or PROFINET IO
System Software for S7-300/400 System and Standard Functions - Volume 1/2
16-6 A5E00709327-01
What are the Effects of FREEZE?
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."
Note
If the DP slaves of the selected group(s) are not currently connected to the network
or have failed when the control command has been sent, they will not be switched
to FREEZE mode. This information will not be communicated in the return value of
the SFC.
Data Consistency
Because SFC 11 "DPSYC_FR" functions are acyclic and can be interrupted by
higher priority classes, you should make sure that the process images are
consistent with the actual inputs and outputs when using SFC 11 "DPSYC_FR".
This is guaranteed if you keep to the following consistency rules:
• Define suitable process image sections for the "SYNC outputs" and the
"FREEZE inputs" (only possible on the S7-400). Call SFC 27 "UPDAT_PO"
immediately before the first call for a SYNC job. Call SFC 26 "UPDAT_PI"
immediately after the last call for a FREEZE job.
• As an alternative: Use only direct I/O access for outputs involved in a SYNC job
and for inputs involved in a FREEZE job. You must not write to these outputs
when a SYNC job is active and not read these inputs when a FREEZE job is
active.
Using SFC 15 and SFC 14
If you use SFC 15 "DPWR_DAT," this SFC must be completed before you send a
SYNC job to the outputs involved.
If you use SFC 14 "DPRD_DAT," this SFC must be completed before you send a
FREEZE job to the inputs involved.