Siemens SIRIUS 3RW5 series - Function Codes 03 (Read Holding Registers) and 04 (Read Input Registers)

Messages and diagnostics
7.2 Function Codes
SIRIUS 3RW5 Modbus TCP communication module
54 Manual, 03/2018, A5E43676481002A/RS-AA/001
7.2.2
Function Codes 03 (Read Holding Registers) and 04 (Read Input Registers)
These functions enable the MODBUS client system to read registers from the 3RW5 register
memory area.
Function Codes 03 and 04 behave in the same way here and supply an identical feedback
signal. A valid offset from the register memory area is expected as the start address. Up to
125 registers per frame can be read.
Request telegram
Address Field
Function Code
Start address
Number of registers
7 bytes
1 byte
2 bytes
2 bytes
- 0x03 0x880F 0x0006
Response telegram
Address Field
Function Code
Number of bytes
Register value
7 bytes
1 byte
1 byte
n registers
- 0x03 0x0C 0x0000 0x2710 0x0000
0x2710 0x0000 0x2710
Example
Reading in the rms phase currents:
● Address field: The address of the 3RW5 soft starter is not entered in the example (-).
● The phase currents start at register address 0x880F and include 6 registers.
● As feedback, the measured values of the current rms phase currents (I L1, I L2, I L3) are
returned with 100 A (0x0000 0x2710) each.
You can find the data table for the measured values in chapter Measured values (Page 86).