Siemens SINAMICS G120 Operating Instructions Manual page 176

Configuring the fieldbus
7.7 Communication via RS485
Table 7- 20
Example
11 h
03 h
00 h
6D h
00 h
02 h
xx h
xx h
The response returns the corresponding data set:
Table 7- 21
Example
11 h
03 h
04 h
11 h
22 h
33 h
44 h
xx h
xx h
Structure of a write request via Modbus function code 06 (FC 06)
Start address is the holding register address.
Using FC 06, precisely one register can always be addressed with one request. The value to
be written to the addressed register is contained in bytes 4 and 5 of the write request.
Table 7- 22
Write request
Incorrect address (a holding register address does not exist)
Write to a "read-only" register
Write to a reserved register
If an incorrect address is entered (a holding register address does not exist), exception code
02 (invalid data address) is returned. An attempt to write to a "read-only" register or a
reserved register is replied to with a Modbus error telegram (exception code 4 - device
failure). In this instance, the detailed internal error code that occurred on the last parameter
access via the holding registers can be read out via holding register 40499.
176
Structure of a read request for slave number 17
Byte Description
0 Slave address
1 Function code
2 Register start address "High" (register 40110)
3 Register start address "Low"
4 Number of registers "High" (2 registers: 40110; 40111)
5 Number of registers "Low"
6 CRC "Low"
7 CRC "High"
Slave response to the read request
Byte Description
0 Slave address
1 Function code
2 Number of bytes (4 bytes are returned)
3 Data of first register "High"
4 Data of first register "Low"
5 Data of second register "High"
6 Data of second register "Low"
7 CRC "Low"
8 CRC "High"
Write request and response of the converter
Converter response
Exception code 02
Modbus error telegram (exception
code 04 - device failure)
Converter with the CU250S-2 Control Unit (vector)
Operating Instructions, 06/2013, FW V4.6, A5E31759476B AB