Siemens SINAMICS G120 Operating Instructions Manual page 159

Parameter value (PWE)
When communication takes place via the USS, the number of PWEs can vary. One PWE is
required for 16 bit values. If 32 bit values are exchanged, two PWEs are required.
Note
U8 data types are transferred as U16, whereby the upper byte is zero. U8 fields, therefore,
require one PWE for each index.
A parameter channel for 3 words is a typical data telegram for exchanging 16 bit data or
alarm messages. The mode with a fixed word length of 3 is used when P2013 = 3.
A parameter channel for 4 words is a typical data telegram for exchanging 32 bit data
variables and requires P2013 = 4.
A parameter channel allowing a flexible word length is used when P2013 = 127. The
telegram length between the master and slave can have a different number of PWEs.
When the length of the parameter channel is fixed (p2013 = 3 or 4), the master must always
transmit either 3 or 4 words in the parameter channel, otherwise the slave will not respond to
the telegram. The response from the slave will also contain either 3 or 4 words. When the
length is fixed, 4 should be used because 3 is insufficient for many parameters (i.e. double
words). When the parameter channel is of a variable length (P2013 = 127), the master
transmits only the amount of words required for the task in the parameter channel. The
length of the response telegram is also restricted to the required size.
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:
● The complete request must be sent in a telegram. Request telegrams cannot be
● If response telegrams contain parameter values, the drive always returns the current
CU240S and CU240E Control Units, FW 3.2
Operating Instructions, 03/2009, A5E02440075B AA
– Evaluating the response ID
– Evaluating the parameter number (PNU)
– Evaluating the parameter index IND, if required
– Evaluating the parameter value PWE, if necessary.
subdivided. The same applies to responses.
parameter value when it repeats response telegrams.
5.11 Operation in fieldbus systems
Functions
159