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Instruction Manual
CVM-C4
7.2.- MODBUS PROTOCOL
In the Modbus protocol, the CVM-C4 device uses the RTU (Remote Terminal Unit) mode.
The Modbus functions implemented in the device are as follows:
Function 0x01: Reading a relay.
Function 0x02: Reading input status.
Function 0x03 and 0x04: Reading integer registers.
Function 0x05: Writing a relay.
Function 0x0F: Writing multiple relays.
Function 0x10: Writing multiple registers.
7�2�1� READING EXAMPLE: FUNCTION 0x01�
Question: Status of output relays
Address Function
Initial
register
No�
of registers
CRC
01 01 0000 0002 BDCB
Address: 01, Peripheral number 1 in decimal.
Function: 01, Read function.
Initial Register: 0000, register on which you want the reading to start.
Nº of registers: 0002, number of registers to read.
CRC: BDCB, CRC character.
Response:
Address Function
No� of
bytes
Register
no� 1:
CRC
01 01 01 03 1189
Address: 01, Responding peripheral number: 1 in decimal.
Function: 01, Read function.
No� of Bytes: 01, No. of bytes received.
Register: 03, in binary it is: 0000 0011, output relays 1 and 2 closed.
CRC: 1189, CRC character.
7�2�2� EXAMPLE OF OPERATION OF THE REMOTE CONTROL: FUNCTION 0x05�
Question: Activate the output of relay 1, programmed to work in remote control mode.
Address Function
Initial
Register
Relay action CRC
01 05 0000 FF00 8C3A
Address: 01, Peripheral number: 1 in decimal.
Function: 05, Writing a relay
Initial Register: 0000, relay 1 address.
Relay action: FF00, We indicate that we want to close the relay.
CRC: 8C3A, CRC Character.
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