Siemens SINAMICS Configuration Manual page 182

Communication
A.1 Communication
The Control Unit uses the following Modbus function codes:
● FC 03: Holding register to read data from the inverter
● FC 06: Write single register to write to individual register
● FC 16: Write to multiple registers to write to several registers
Structure of a Modbus TCP message
Transaction ID
Figure A-38
Structure of a read request via Modbus function code 03 (FC 03)
Any valid register address is permitted as the start address.
Via FC 03, the control can address more than one register with one request. The number of
addressed registers is contained in bytes 10 and 11 of the read request.
Table A-17
Value
MBAP header
03 h
00 h
6D h
00 h
02 h
The response returns the corresponding data set:
Table A-18
Value
MBAP header
03 h
04 h
11 h
22 h
33 h
44 h
182
Modbus Application Header
Protocol ID
2 Bytes 2 Bytes
Individual components, including Modbus Application Header (MBAP) and function code
Structure of a read request for device number 17, example
Byte Description
7
8 Register start address "High" (register 40110)
9 Register start address "Low"
10 Number of registers "High" (2 registers: 40110; 40111)
11 number of registers "Low"
Device response to the read request, example
Byte Description
7
8 Number of bytes (4 bytes are returned)
9 Data first register "High"
10 Data first register "Low"
11 Data second register "High"
12 Data second register "Low"
Application Data Unit (ADU)
Unit ID
Length FCode
2 Bytes 1 Byte 1 Byte
Configuration Manual, 08/2017, A5E36912609A
Protocol Data Unit (PDU)
Data
0 ... 252 Bytes
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