Entry type: FAQ, Entry ID: 2121979, Entry date: 04/20/2000
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Transfer of analog values from and to the PROFIBUS DP slave

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QUESTION:
The analog values are transferred only in part or not at all. How can I clear this problem?

ANSWER:
If none or only part of the analog values are transferred, or the transferred values are incorrect, then this might have something to do with the length of the consistent data of the slave (affects S7-300/400 CPUs).
If more than 4 bytes (or exactly 3 bytes) are consistent over the entire length, then you must access the analog values of the slave with the SFCs 14 "DPRD_DAT" and 15 "DPWR_DAT". A description of the SFCs is given in the manual "System Software for S7-300/400 System and Standard Functions". The information on consistent data lengths of the PROFIBUS DP slave are given in the HW Config.
Procedure:

  1. In the HW Config you mark the PROFIBUS slave.

  1. Double-click the module from which you want to know which consistent areas it has. In the "Address/ID" tab of the "Properties - DP slave" window you can see the length over which the data is consistent.