Siemens Sinamics S110 Function Manual page 652

Communication
9.5 Communication using USS
Parameter value (PWE)
With communication over USS, the number of PWEs can vary. One PWE is required for 16-
bit values. Two PWEs are required if 32-bit values are exchanged.
Note
U8 data types are transferred as U16 with the upper byte set to zero. U8 fields therefore
require one PWE per index.
A parameter channel of 3 words represents a typical data telegram for exchanging 16-bit
data or alarms. The mode with a fixed word length of 3 is used when p2023 = 3.
A parameter channel for 4 words is a typical data telegram for exchanging 32-bit data
variables and requires p2023 = 4.
A parameter channel with a variable length is used with p2023 = 127. The telegram length
between the master and slave can vary in terms of the number of PWEs.
When the length of the parameter channel is fixed (p2023 = 3 or 4), the master must always
send either 3 or 4 words in the parameter channel accordingly. Otherwise the slave will not
respond to the telegram. The response of the slave will also comprise 3 or 4 words. For a
fixed length, 4 should be used because 3 is insufficient for many parameters (i.e. double
words). For a variable length of parameter channel (p2023 = 127), the master will only send
the number of words necessary for the task in the parameter channel. The response
telegram is also no longer than necessary.
Rules for editing 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
650
– Evaluating the response identifier
– Evaluating the parameter number (PNU)
– Evaluating the parameter index (IND), if necessary, or
– Evaluating the parameter value PWE, if necessary.
subdivided. The same applies to responses.
parameter value when it repeats response telegrams.
Function Manual, 01/2011, 6SL3097-4AB10-0BP3
Function Manual