Connection to a fieldbus
6.4 Communication via RS485
Inverter with CU240B-2 and CU240E-2 Control Units
Operating Instructions, 07/2010, FW 4.3.2, A5E02299792B AA
139
Parameter value (PWE)
You can vary the number of PWEs using parameter p2023.
Parameter channel with fixed length
Parameter channel with variable length
P2023 = 4
A parameter channel with fixed length should
contain 4 words as this setting is sufficient for all
parameters (including double words).
P2023 = 3
You can select this setting if you only want to
read or write 16-bit data or alarm signals.
16-bit data: e.g. p0210 supply voltage
32-bit data:
Indexed parameter, e.g. p0700[0…n]
Bit parameter, e.g. 722.0...12)
The master must always transmit the
permanently set number of words in the
parameter channel. Otherwise the slave will not
respond to the telegram.
When the slave responds it must always respond
with the defined number of words.
P2023 = 127
For a variable length of parameter channel, the
master will only send the number of PWEs
necessary for the task in the parameter channel.
The response telegram is also no longer than
necessary.
Note
8-bit values are transmitted as 16-bit values; the higher-order byte is zero. The fields of 8-bit
values require one PWE per index.
Rules for editing requests/responses
● You can only request one parameter for each telegram sent.
● Each received telegram contains only one response.
● The master must repeat a request until it receives a suitable response.
● Request and response are assigned to one another using the following identifiers:
– Suitable response identifier
– Suitable parameter number
– Suitable parameter index IND, if required
– Suitable parameter value PWE, if necessary
● The master must send the complete request in one telegram. Request telegrams cannot
be split up. The same applies to responses.