Communication
6.6 Communication via USS
Control Units CU240S
178
Operating Instructions, 07/2008 - FW 3.2, A5E00766042B AD
6.6.3
Structure of a USS Telegram
Description
The following figure shows the structure of a typical USS telegram.
STX LGE ADR 1
.
2
.
n
. BCC
: : :
6WDUW'HOD\
866IUDPH
n use data
Trailer
Header
Figure 6-16 Structure of USS telegram
Variable length telegrams and fixed length telegrams can both be used. This can be selected
using parameters P2012 and P2013 to define the PZD and PKW lengths.
The most common fixed length application is shown below:
STX
1 Byte
LGE
1 Byte
ADR
1 Byte
PKW
8 Bytes (4 Words: PKE + IND + PWE1 + PWE2)
use data
PZD
4 Bytes (2 Words: PZD1 + PZD2)
BCC
1 Byte
Sum :
16 Bytes (LGE indicates 14 bytes as STX and LGE are not counted in LGE)
Start Delay
The length of the start delay is at least the time of two characters and depends on the
baudrate.
Table 6-40 Length of start delay
Baudrate in bit/s Transfer time per character (= 11 bit)
Transfer time per bit Min. Start Delay
9600
1.146 ms
104.170 µs
> 2.291 ms
19200
0.573 ms
52.084 µs
> 1.146 ms
38400
0.286 ms
26.042 µs
> 0.573 ms
57600
0.191 ms
17.361 µs
> 0.382 ms
115200
0.059 ms
5.340 µs
> 0.117 ms
Note: The time between characters must be smaller than the start delay.
