Connection to a fieldbus
6.3 Communication via PROFIBUS
Inverter with CU240B-2 and CU240E-2 Control Units
122
Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA
Example of read request for parameter P7841[2]
To obtain the value of the indexed parameter P7841, you must fill the telegram of the
parameter channel with the following data:
● Request parameter value (field): Bits 15 … 12 in the PKE word:
Request identifier = 6
● Parameter number without offset: Bits 10 … 0 in the PKE word:
Because you can only code parameter numbers from 1 … 1999 in the PKE, you must
deduct as large an offset as possible, a number divisible by 2000, from the parameter
number, and transfer the result of this calculation to the PKE word.
In our example, this means: 7841 - 6000 = 1841
● Coding the offset of the parameter number in the page index byte of the IND word:
In this example: When offset = 6000, this corresponds to a page index value of 0x90.
● Index of parameter in the subindex byte of the IND word:
In this example: Index = 2
● Because you want to read the parameter value, words 3 and 4 in the parameter channel
for requesting the parameter value are irrelevant. They should be assigned a value of 0,
for example.
Table 6- 17 Request to read parameter P7841[2]
PKE (1st word)
IND (2nd word)
PWE (3rd and 4th words)
AK
PNU (10 bits)
Subindex
(H byte)
Page index
(L byte)
PWE1
(high-order
word)
PWE2
(low-order
word)
0x6
0
0x731 (decimal: 1841)
0x02
0x90
0x0000
0x0000
Rules for editing requests and responses
● You can only request one parameter per transmitted telegram
● Each received telegram contains only one response
● The request must be repeated until the right response is received
● The response is assigned to a request by means of the following identifiers:
– Suitable response identifier
– Suitable parameter number
– Suitable parameter index IND, if required
– Suitable parameter value PWE, if necessary
● The complete request must be sent in a telegram. Request telegrams cannot be
subdivided. The same applies to responses.