Modbus-Rtu 1/2/ Channel 12V Relay Module Switch Modbus RTU 4 Channel Relay Output 12V Switch Input 485 Communication TTL Pin He

1, VCC, GND: dc7-24v power input;
2, IN, GND: dc3.3-30v optocoupler signal input;
3, A+, B- : RS485 communication interface, A+, B- connect to external control terminal A+, B-;
4. Relay switch signal output:
NC: normally closed end, short connection with COM before the relay closes, and suspension after the relay closes;
COM: common terminal;
NO: normal start, suspended before relay suction, short connection with COM after suction.
5. Relay indicator light: it is lit when the relay is closed;
GND, RXD, TXD: TTL level UART communication interface, GND, RXD, TXD are connected to GND, TXD, RXD of external control terminal respectively;

3. Introduction to Modbus RTU command
Modbus devices perform related operations by receiving Modbus RTU instructions from external control terminals (such as upper computer /MCU). A frame instruction is generally composed of device address, function code, register address, register data and check code, and the frame length is related to the function code. Generally, the first byte of each frame data is the device address, and the range can be set to 1-255, with the default of 255 (i.e. 0xFF), and the last 2 bytes are CRC checksum codes.
Assuming the device address is 255, the common Modbus RTU instructions are as follows: