Operating instructions

Functions
5.11 Operation in fieldbus systems
CU240S and CU240E Control Units, FW 3.2
182 Operating Instructions, 03/2009, A5E02440075B AA
Table 5- 83 Coding example for a parameter number in PKE and IND for P7841, index 2
PKE IND
decimal xx 1841 144 2
hex xx 731 90 02
Parameter value (PWE) 3rd and 4th word
When data is transferred via PROFIBUS or PROFINET, the parameter value (PWE) is
transferred as a double word (32 bit). Only one parameter value can be transferred in a
single telegram.
A 32 bit parameter value includes PWE1 (high-order word, third word) and PWE2 (low-order
word, fourth word).
A 16 bit parameter value is transferred in PWE2 (low-order word, fourth word). In this case,
PWE1 (high-order word, third word) must be set to 0 in the PROFIBUS DP master /
PROFINET I/O controller.
Rules for processing requests/responses
● A request or a response can only be referred to one parameter.
● The master must constantly repeat a request until it receives a suitable response.
● The master recognizes the response to a request that it sent by:
– Evaluating the response ID
– Evaluating the parameter number (PNU)
– Evaluating the parameter index IND, if required
– Evaluating the parameter value PWE, if necessary.
● The complete request must be sent in a telegram. Request telegrams cannot be
subdivided. The same applies to responses.
● If response telegrams contain parameter values, the drive always returns the current
parameter value when it repeats response telegrams.