Modbus Protocol

This device communicates using the Modbus RTU protocol over the RS-485 standard.

Device Address

This device's preconfigured user-definable address is 0x18. Users can change the address using the holding registers.

Modbus Function Codes

The following Modbus function codes are functional with this device.

Command Register	Function	Description	Bytes
0x03	Read holding registers	Returns configuration parameters	2
0x04	Read input registers	Returns measured readings and statistics	2
0x06	Write single register	Writes a single configuration parameter	2
0x10	Write multiple registers	Writes multiple configuration parameters	2 x N

Device Registers

The following registers are available with this device.

Register Type	Register Address	Description	Bytes
Input Register (R)	0x0001	Temperature (Actual)	2
Input Register (R)	0x0002	Temperature (Average)	2
Input Register (R)	0x0003	Temperature (Min)	2
Input Register (R)	0x0004	Temperature (Max)	2
Input Register (R)	0x0005	Temperature (Std. Dev.)	2
Input Register (R)	0x0006	Relative Humidity (Actual)	2
Input Register (R)	0x0007	Relative Humidity (Average)	2
Input Register (R)	0x0008	Relative Humidity (Min)	2
Input Register (R)	0x0009	Relative Humidity (Max)	2
Input Register (R)	0x000A	Relative Humidity (Std. Dev.)	2
Input Register (R)	0x000B	Pressure (Actual)	2
Input Register (R)	0x000C	Pressure (Average)	2
Input Register (R)	0x000D	Pressure (Min)	2
Input Register (R)	0x000E	Pressure (Max)	2
Input Register (R)	0x000F	Pressure (Std. Dev.)	2
Input Register (R)	0x0010	Device Pitch (Actual)	2
Input Register (R)	0x0011	Device Roll (Actual)	2
Input Register (R)	0x0012	Device Temperature	2
Holding Register (R/W)	0x0101	Device Address	2
Holding Register (R/W)	0x0102	Baud Rate	2
Holding Register (R/W)	0x0103	Statistics Period (Secs)	2
Holding Register (R/W)	0x0104	IMU Correction (Pitch)	2
Holding Register (R/W)	0x0105	IMU Correction (Roll)	2
Holding Register (R/W)	0x0106	Temperature Correction 1	2
Holding Register (R/W)	0x0107	Temperature Correction 2	2
Holding Register (R/W)	0x0108	Temperature Correction 3	2
Holding Register (R/W)	0x0109	RH Correction 1	2
Holding Register (R/W)	0x010A	RH Correction 2	2
Holding Register (R/W)	0x010B	RH Correction 3	2
Holding Register (R/W)	0x010C	Pressure Correction 1	2
Holding Register (R/W)	0x010D	Pressure Correction 2	2
Holding Register (R/W)	0x010E	Pressure Correction 3	2

Communication Syntax

Reading sensor data

The host device can read one or more sensor data by calling the starting register address.

Request from the host: Device address [1 Byte] + Function code (0x04) [1 Byte] + Input register start address [2 Bytes MSB first] + Requested register length [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Response from the device: Device address [1 Byte] + Function code (0x04) [1 Byte] + Response register length in Bytes [1 Byte] + Register 1 [2 Bytes MSB first] + Register N [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Reading configuration register

The host device can read one or more configuration registers by calling the starting register address.

Request from the host: Device address [1 Byte] + Function code (0x03) [1 Byte] + Holding register start address [2 Bytes MSB first] + Requested register length [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Response from the device: Device address [1 Byte] + Function code (0x03) [1 Byte] + Response register length in Bytes [1 Byte], Register 1 [2 Bytes MSB first] + Register N [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Writing single configuration register

The host device can write one configuration register.

Command from the host: Device address [1 Byte] + Function code (0x06) [1 Byte] + Holding register address [2 Bytes MSB first] + Value to be set [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Response from the device: Device address [1 Byte] + Function code (0x06) [1 Byte] + Holding register address [1 Byte] + Value set [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Writing multiple configuration registers

The host device can write multiple configuration registers.

Command from the host: Device address [1 Byte] + Function code (0x10) [1 Byte] + Holding register start address [2 Bytes MSB first] + Requested register length [2 Bytes] + Configuration values length in Bytes [1 Byte] + Value to be set 1 [2 Bytes MSB first] + Value to be set N [2 Bytes MSB first] + CRC [2 Bytes MSB first]

Response from the device: Device address [1 Byte] + Function code (0x10) [1 Byte] + Holding register start address [1 Byte], Value set [2 Bytes MSB first], CRC [2 Bytes MSB first]