Trox Technik FSL-CONTROL II Installation And Configuration Manual page 66

Modbus functions
The device includes the following functions:
Function 1 (0x01) Read Coils
Function 3 (0x03) Read Holding Registers
Function 4 (0x04) Read Input Registers
Function 5 (0x05) Write Single Coil
Function 6 (0x06) Write Single Register
Function 8 (0x08) Diagnostics
Function 16 (0x10) Write Multiple Registers
Function 43/14 (0x02B/0x0E) Read Device Identification
The encoding for the corresponding Modbus RTU frames is shown below (shown
without CRC). For data with 2 bytes the High-Byte comes first.
Meaning of exception codes:
1 Illegal function code
2 Illegal Data Address
3 Illegal Data Value
Modbus function 3 (0x03) Read Holding Registers
Modbus function 4 (0x04) Read Input Registers
These functions are used to read several consecutive registers. Both functions
are identical.
Request:
Byte 0 Slave Address
Byte 1 Function Code
Byte 2-3 Register Address
Byte 4-5 Register Quantity
Response:
Byte 0 Slave Address
Byte 1 Function Code
Byte 2 Byte Count
Byte 3-4 Register Value
Byte ... Register Value
Error:
Byte 0 Slave Address
Byte 1 Error Code
Byte 2 Exception Code
Unknown code for this function or subfunction.
Invalid register address.
Inconsistent encoding in the number of registers,
number of bytes, data value.
Single room control system FSL‑CONTROL II
Rotary switch 1-99
0x03 / 0x04
First register
No. of registers
Rotary switch 1-99
0x03 / 0x04
2 bytes per register
0x0000-0xFFFF
0x0000-0xFFFF
Rotary switch 1-99
0x83 / 0x84
0x02,0x03
2