Upper Limit For The Transmission Of Consistent User Data On A Dp Slave - Siemens SIMATIC S7-400H Manual

Installation of a CPU 41x-H

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.
4-46
Automation System S7-400H Fault-tolerant Systems
A5E00068197-07