Uss Parameter Channel - Siemens SINAMICS CU240S DP-F Operating Instructions Manual

The length of the parameter channel is determined by parameter P2013, that for the process
data by parameter P2012. If either no parameter channel or no PZD is required, the
corresponding parameters can be set to zero ("PKW only" or "PZD only" respectively).
It is not possible to transmit "PKW only" and "PZD only" alternatively. If both channels are
required they must be transferred together.
6.6.5

USS Parameter Channel

Parameter channel
The USS protocol defines for the inverters, the use data structure with which a master can
access the inverter slaves. The parameter channel can be used to monitor and/or change
any parameter in the inverter. For detailed information, refer the section "Data Structure of
the Parameter Channel".
Figure 6-18
Parameter value (PWE)
For acyclic communication via USS, the number of PWEs can vary. For 16 bit values one
PWE is required. If 32 bit values are exchanged, two PWEs are required.
Note
Data types U8 will be transferred as U16 with the upper byte zero. Arrays of U8 will therefore
require one PWE per index.
A parameter channel for 3 words is a typical data frame for exchanging 16 bit data or alarm
messages. The mode with a fixed word length of 3 is used with p2013 = 3.
A parameter channel for 4 words is a typical data frame for exchanging 32 bit data variables
and requires p2013 = 4.
A parameter channel for a flexible word length is used with p2013 = 127. The length for
telegrams between master and slave can have a different number of PWEs.
If the length of the parameter channel is fixed (p2013 = 3 or 4), then the Master must always
correctly send either 3 or 4 words in the parameter channel. Otherwise, the slave will not
respond to the telegram. The slave response will be either 3 or 4 words as well. If a fixed
length is used, this should be 4, as 3 would not be sufficient to support many of the
parameters (i.e. double words). For variable length of the parameter channel (p2013 = 127)
the master sends only the necessary number of words for the task in the parameter channel.
The length of the response telegram will also only be as long as necessary.
Control Units CU240S
Operating Instructions, 07/2008 - FW 3.2, A5E00766042B AD
Structure of the parameter channel in the telegram structure
Communication
6.6 Communication via USS
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