Write And Read Access Using Function Codes - Siemens SINAMICS G110M Function Manual

5.4.6

Write and read access using function codes

Basic structure of read and write access using function codes
Function codes used
For data exchange between the master and slave, predefined function codes are used for
communication via Modbus.
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 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 4 and 5 of the read request.
Table 5- 18
Value
11 h
03 h
00 h
6D h
00 h
02 h
xx h
xx h
Fieldbuses
Function Manual, 04/2018, FW V4.7 SP10, A5E34229197B AE
Structure of a read request via slave number 17, example
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"
Communication via RS485
5.4 Communication using Modbus RTU
137