Writing Data Consistently To A Dp Standard Slave Using Sfc 15 "Dpwr_Dat" - Siemens SIMATIC S7-400 Reference Manual

Structure of a CPU 41x
1.13.4 Writing Data Consistently to a DP Standard Slave Using SFC 15
"DPWR_DAT"
Using SFC 15 "DPWR_DAT" (write consistent data to a DP standard slave) you
can consistently write data to the DP standard slave addressed in the RECORD.
The source range must have the same length as the one you have configured for
the selected module with STEP 7.
Note
The Profibus DP standard defines the upper limit for the transmission of consistent
user data (see following section). Typical DP standard slaves adhere to this upper
limit. In older CPUs (<1999) there are restrictions in the transmission of consistent
user data depending on the CPU. For these CPUs you can determine the
maximum length of the data which the CPU can consistently read and write to and
from the DP standard in the respective technical specifications under the index
entry "DP Master – User data per DP slave". Newer CPUs are capable of
exceeding the value for the amount of data that a DP standard slave can send and
receive.
Upper Limit for the Transmission of Consistent User Data on a DP Slave
The Profibus DP standard defines the upper limit for the transmission of consistent
user data to a DP slave. For this reason a maximum of 64 words = 128 bytes of
user data can be consistently transferred in a block to the DP slave.
During the configuration you can determine the size of the consistent area. You
can set a maximum length of consistent data at 64 words = 128 bytes in the
special identification format (SKF) (128 bytes for inputs and 128 bytes for outputs);
the data block size cannot exceed this.
This upper limit only applies to pure user data. Diagnostics and parameter data are
regrouped into full records and therefore always transferred consistently.
In the general identification format (AKF) the maximum length of consistent data
can be set at 16 words = 32 bytes (32 bytes for inputs and 32 bytes for outputs);
the data block size cannot exceed this.
Note in this context that a CPU 41x in a general environment acting as a DP slave
on a third-party master (connection defined by GSD) has to be configured with the
general identification format. The transfer memory of a CPU 41x acting as a DP
slave to the PROFIBUS DP can therefore be a maximum of 16 words = 32 bytes.
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Automation System S7-400 CPU Specifications
A5E00165965-01