Circutor CEM-C31-485-DS, Instruction Manual

Page: 42 / 58

7�2�2�- MODBUS PROTOCOL
The MODBUS protocol is a communication standard in the industry that enables the network
connection of multiple devices, where there is a master and multiple slaves. Within the
MODBUS protocol the CEM-C31-485-xx uses the RTU (Remote Terminal Unit) mode.
In RTU mode, message starts and ends are detected with silences of at least 3.5 characters,
and the 16-bit CRC error-detection method is used.
The MODBUS functions implemented in the device are:
Functions 03 and 04 . Reading registers.
Function 10 . Writing multiple registers.
7�2�2�1�- Read commands
The CEM-C31-485-xx supports integer type read functions: 0x03 and 0x04.
Example:
Reading of the device’s serial number with peripheral number 01.
We will send the following Modbus frame:
Address Function
Initial
register
Register
no�
CRC
01 04 2710 0002 CRC
The device will respond to us with the next frame:
Address Function No� of bytes Serial no� CRC
01 04 04 XXXX XXXX CRC
Note: The values are shown in hexadecimal.
The number of requested registers must be the same as the size of the variable requested.
It is possible to read several consecutive addresses, if the request meets the correct format.
7�2�2�2�- Write commands
The CEM-C31-485-xx supports integer type write Functions: 0x10.
Example:
Changing the Modbus address of peripheral 01 to the address 0x000A .
We will send the following Modbus frame:
Address Function
Initial
register
Register
no�
No� bytes Data CRC
01 10 03E8 0001 02 000A CRC
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CEM-C31
Instruction Manual