Siemens COMBIMASTER 411 Operating Instructions Manual page 29

Issue 03/02
Rules for processing requests/responses
Ø A request or a response can only ever refer to one parameter.
Ø The master must repeat a request continuously until it has received the
appropriate response.
Ø The master detects the response to a request it has sent by
♦ evaluating the response identifier,
♦ evaluating the parameter number PNU,
♦ evaluating the parameter index IND if necessary, or
♦ evaluating the parameter value PWE if necessary.
Ø The complete request must be sent in one telegram. Request telegrams
cannot be split. The same applies to responses.
Ø In the case of response telegrams which contain parameter values, the drive
always returns the momentary parameter value when repeating response
telegrams.
Ø If no information needs to be fetched from the PKW interface in cyclical
operation (only PZD data are relevant), then the "No request" request telegram
must be issued.
PROFIBUS Communication Module
6SE6400-5AV00-0BP0
Operating instructions
COMMUNICATION
29