Siemens SINAMICS V20

Communicating with the PLC
7.2 MODBUS communication
SINAMICS V20 Converter
180 Operating Instructions, 10/2019, A5E34559884-012
Supported Function Codes
The SINAMICS V20 supports only three Function Codes. If a request with an unknown
Function Code is received, an error message will be returned.
FC3 - Read Holding Registers
When a message with FC = 0x03 is received, then 4 bytes of data are expected, that is, FC3
has 4 bytes of data:
● 2 bytes for the starting address of register
● 2 bytes for the number of registers
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Address FC (0x03)
Start address
Number of registers
CRC
High
Low
High
Low
High
Low
Converter response
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
...
Byte N*2 - 1
Byte N*2
Byte N*2 + 1
Byte N*2 + 2
Address FC (0x03) Number
of bytes
Register 1 value
...
Register N value
CRC
High Low High Low High Low
FC6 - Write Single Register
When a message with FC = 0x06 is received, then 4 bytes of data are expected, that is, FC6
has 4 bytes of data:
● 2 bytes for the starting address of register
● 2 bytes for the register value
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Address FC (0x06)
Start address
New register value
CRC
High
Low
High
Low
High
Low
Converter response
Byte 1
Byte 2
Byte 3
Byte 4
Byte 5
Byte 6
Byte 7
Byte 8
Address FC (0x06)
Start address
New register value
CRC
High
Low
High
Low
High
Low