Siemens SINAMICS V20

Communicating with the PLC
7.1 USS communication
SINAMICS V20 Converter
176 Operating Instructions, 10/2019, A5E34559884-012
The messages are always sent in the following format (half-duplex communication):
● Response delay time: 20 ms
● Start delay time: depends on baud rate (minimum operation time for 2-character string:
0.12 to 2.3 ms)
● Message transfer sequence:
– master polls slave 1, then slave 1 responds
– master polls slave 2, then slave 2 responds
● Fixed framing characters that cannot be altered:
– 8 data bits
– 1 parity bit
– 1 or 2 stop bits
Abbreviation
Significance
Length
Explanation
STX
Start of text
ASCII characters
02 hex
LGE
Telegram length
1 byte
Contains the telegram length
ADR Address 1 byte Contains the slave address and the
telegram type (binary coded)
1. ...... n. Net characters Each 1 byte Net data, contents are dependent on the
request
BCC
Block check character
1 byte
Data security characters
Request and response IDs
Request and response IDs are written in bits 12 to 15 of the PKW (parameter ID value) part
of USS telegram.
Request IDs (master → slave)
Request ID
Description
Response ID
positive
negative
0
No request
0
7/8
1
Request parameter value
1/2
7/8
2
Modify parameter value (word)
1
7/8
3 Modify parameter value (double word) 2 7/8