Technical data

Table Of Contents
SFCs for Distributed I/Os or PROFINET IO
System Software for S7-300/400 System and Standard Functions - Volume 1/2
A5E00709327-01
16-5
Writing Outputs of DP Modules
The writing of outputs of DP modules is triggered as follows:
By transfer commands to the DP I/Os,
By writing the process image output table to the modules (by the operating
system at the end of OB1 or by calling SFC 27 "UPDAT_PO"),
By calling SFC 15 "DPWR_DAT."
In normal operation, the DP master transfers the output bytes cyclically (within the
cycle of the PROFIBUS DP bus) to the outputs of the DP slaves.
If you want to have certain output data (possibly distributed on several slaves)
applied to the outputs to the process at exactly the same time, you can send the
SYNC command to the relevant DP master using SFC 11 "DPSYC_FR."
What are the Effects of SYNC?
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."
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 SYNC mode. This information will not be communicated in the return value of
the SFC.
Reading Input Data of DP Modules
The input data of the DP modules are read as follows:
Using load commands to the DP I/Os,
When the process image input table is updated (by the operating system at the
start of OB1 or by calling SFC 26 "UPDAT_PI"),
By calling SFC 14 "DPRD_DAT."
In normal operation, the DP master receives this input data cyclically (within the
cycle of the PROFIBUS DP bus) from its DP slaves and makes them available to
the CPU.
If you want to have certain input data (possibly distributed on several slaves) to be
read from the process at exactly the same time, send the FREEZE control
command to the relevant DP master using SFC 11 "DPSYC_FR."