7�2�- Modbus Protocol; 7�2�1�- Modbus Query Example - Circutor Line-CVM-D32 Instruction Manual

7�2�- MODBUS PROTOCOL
The MODBUS protocol is a standard communications protocol in industry enabling networking of mul-
tiple devices, involving a master and multiple slaves. It enables individual master-slave dialogue and
also allows commands in broadcast format.
The MODBUS protocol used by the line-CVM-D32 device implements the RTU (Remote Terminal Unit)
mode.
In RTU mode, message start and end are detected with a 3.5 minimum character silence and the 16-bit
CRC error detection method is used.
The MODBUS functions implemented in the device are:
Function 0x04 and 0x03: Register readout.
Function 0x02: Input status readout.
Function 0x10: Writing multiple registers.
Function 0x01: Relay status readout
Function 0x05: Writing a relay status.
7�2�1�- MODBUS QUERY EXAMPLE
Question: Instantaneous value of L1 phase voltage.
Address: 0A, Peripheral number: 10 en decimal.
Function: 04, Read function.
Initial register: 0000, desired register to start readout.
Nº of registers: 0002, number of registers to read.
CRC: xxxx, CRC character.
Response:
Address: 0A, Number of peripheral responding: 10 in decimal.
Function: 04, Read function.
No� of bytes: 04, No. of bytes received.
Register: 0000084DL1 phase voltage value: VL1 x 10 : 212.5V
CRC: xxxx, CRC character.
70
Address Function
0A 04
Address Function No� of bytes
0A 04
Initial No� of
register registers
0000 0002
Register no� 1 Register no� 2
04 0000
line-CVM-D32
CRC
xxxx
CRC
084D xxxx
Instruction Manual