Data Sheet

Copyright © Roboteq Inc. 2018. All Rights Reserved. 4
3
Read Holding Registers
4
Read Input Registers
5
Write Single Coil
6
Write Single Holding Register
15
Write Multiple Coils
16
Write Multiple Holding Registers
2. Roboteq Implementation
Roboteq’s implementation of Modbus doesn’t contain all supported functions and modes but contains only
subset of it. I this section we are introducing the supported modes and functions implemented in
Roboteq’s micro controllers.
2.1 Supported Functions
Controllers only supports two functions:
2.1.1 Read Input Registers (0x04)
This function is implemented to read exactly 4 bytes (2 registers). Issuing any messages to read other than
2 registers will return no response.
For examples, to read VAR1, you need to read 2 registers from address 0x20C1 so you need to send the
following RTU message:
01 04 20 C1 00 02 2B F7
Name
Description
01
Node address
04
Function code (Read Input Registers)
20 C1
Register address for reading VAR1
00 02
Length of registers to be read (must be 2)
2B F7
Cyclic redundancy check (CRC-16-IBM)
The response for this message will be as following:
01 04 04 00 00 12 34 F6 F3
Name
Description
01
Node address
04
Function code (Read Input Registers)
04
Total bytes read (always 4 bytes)