Siemens SINAMICS G120 Operating Instructions Manual page 228

Functions
8.7 Communication via USS
Table 8-14
Parameter value (PWE)
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 PKW area for 3 words is a typical data frame for exchanging 16 bit data or alarm
messages. The mode with a fixed PZD length of 3 is used with p2013 = 3.
A PKW area for 4 words is a typical data frame for exchanging 32 bit data variables and
requires p2013 = 4.
A PKW area for a flexible PZD 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 PKW is fixed (p2013 = 3 or 4), then the Master must always correctly send
either 3 or 4 words in the PKW area (if not, the slave will not respond to the telegram). The
slave response PKW 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 PKW (p2013 = 127) the Master sends only the necessary number of words
for the task in the PKW area. The length of the response telegram will also only be as long
as necessary.
8-32
Example coding for parameter no. in PKE and IND for P8820, Index 16
decimal xx
hex xx
PKE
820
334
Operating Instructions, 11/2006, A5E00766042B AA
IND
8000 16
20 10
Control Units CU240S