SeeedStudio SenseCAP ONE S500 5-in-1 Compact Weather Sensor : User Manual : Page 27

User manual/ Technical information

The 27 Page total 50

Modbus-RTU Protocol

To start Modbus-RTU communication, the M12 data cable of the device needs to be connected

to the RS-485 port of one Data Logger, which powers up the device at a voltage of 12V-24V. The

following image is a diagram of the wiring:

Protocol communication parameters

Data Format One start bit, 8 Data bits, None parity, one Stop bits.

Baud Rate 9600bps (default), which can be modified by configuration.

Default Device Address 0x01

4.1.1 Modbus-RTU Protocol Message Format

Sensor data is stored in the Input Register and is read-only

The device address and the communication baud rate of RS-485 are stored in the Holding

Register and can be modified.

Each register is 16bits and takes up 2 bytes.

Read the message from the input register.

The message format from by the host

Slave address Function code Register address Number of registers CRC check

1 byte 1 byte 2 bytes (big-endian). 2 Byte (big-endian). 2 bytes

AA 0x04 RRRR NNNN CCCC

Address 0-247 0x04 big endian big endian little endian