Siemens Micromaster Profibus - Rules for Processing Requests;Responses

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PROFIBUS Optional Board Operating instructions
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½ A request or a response can only ever refer to one parameter.
½ The master must repeat a request continuously until it has received the
appropriate response.
½ 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.
½ The complete request must be sent in one telegram. Request telegrams
cannot be split. The same applies to responses.
½ In the case of response telegrams which contain parameter values, the drive
always returns the momentary parameter value when repeating response
telegrams.
½ 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.