SEN0658 Ultrasonic RS485 Weather Sensor Reference: API, Protocol & Pinout

This article delves into the RS485 communication protocol, explaining data frame formats, Modbus-RTU usage, and providing practical examples for sensor data communication.

Communication Protocol Description

1. Basic communication parameters

Interface	Encoding	Data bits	Parity bits	Stop bits	Error checking	Baud rate
RS485	8-bit binary	8	None	1	CRC	1200bit/s, 2400bit/s, 4800bit/s, 9600bit/s, 19200bit/s, 38400bit/s, 57600bit/s, 115200bit/s configurable, default 4800bit/s

2. Data frame format definition

Using Modbus-RTU communication protocol, the format is as follows:

Initial structure ≥4 bytes of time

Address code = 1 byte

Function code = 1 byte

Data area = N bytes

Error check = 16-bit CRC code

End structure ≥4 bytes of time

Address code: The address of the sensor, which is unique in the communication network (factory default 0x01).

Function code: The function indication of the command sent by the host. This sensor reads the register function code 0x03 and writes the register function code 0x06

Data area: The data area is the specific communication data. Note that the high byte of 16-bit data is in front!

CRC code: A two-byte check code.

Host inquiry frame structure:

Address code	Function code	Register start address	Register length	Check code low bit	Check code high bit
1byte	1byte	2byte	2byte	1byte	1byte

Slave response frame structure:

Address code	Function code	Number of valid bytes	Data area 1	Data area 2	Nth data area	Check code
1byte	1byte	1byte	2byte	2byte	2byte	2byte

General register address

Register address	PLC or configuration address	Content	Supported function code	Definition description
01F4H	40501	Wind speed value	0x03	10 times the actual value
01F6H	40503	Wind direction (0-7 gears)	0x03	Actual value (0 for due north, increasing value clockwise, 2 for due east)
01F7H	40504	Wind direction (0-360°)	0x03	Actual value (0° for due north, increasing value clockwise, 90° for due east)
01F8H	40505	Humidity value	0x03	10 times the actual value
01F9H	40506	Temperature value	0x03	10 times of actual value
01FAH	40507	Noise value	0x03	10 times of actual value
01FBH	40508	PM2.5 value	0x03	Actual value
01FCH	40509	PM10 value	0x03	Actual value
01FDH	40510	Atmospheric pressure value	0x03	Actual value
01FEH	40511	High 16 bits of illumination value	0x03	Actual value
01FFH	40512	Low 16 bits of illumination value	0x03	Actual value
0200H	40513	Illumination value	0x03	Actual value
0201H	40514	Rainfall value	0x03	10 times the actual value
07D0H	42001	Device address	0x03/0x06	1~254 (factory default 1)
07D1H	42002	Device baud rate	0x03/0x06	0 represents 2400, 1 represents 4800, 2 represents 9600, 3 represents 19200, 4 represents 38400, 5 represents 57600, 6 represents 115200, 7 represents 1200

Calibration register address

Register address	Content	Supported function code	Definition description
6000H	Wind direction offset register	0x06	0 represents the normal direction, 1 represents the direction offset by 180 degrees
6001H	Wind speed zeroing register	0x06	Write 0xAA, wait for 10 seconds, and the device will be zeroed
6002H	Rainfall zeroing register	0x06	Write 0x5A, and the rainfall value will be zeroed

3. Communication protocol example and explanation

3.1. Read the wind speed value of a single register

Inquiry frame: Read value function code 0x03

Address code	Function code	Register start address	Register length	Check code low bit	Check code high bit
0x01	0x03	0x00 0xF4	0x00 0x01	0xC4	0x04

Response frame:

Address code	Function code	Return valid bytes	Wind speed value	Check code low bit	Check code high bit
0x01	0x03	0x02	0x00 0x7D	0x78	0x65

Wind speed value:

007D (hexadecimal) = 125=> Wind speed value = 1.25m/s

3.2, read multiple register humidity and temperature values

Inquiry frame: read numerical function code 0x03

Address code	Function code	Register start address	Register length	Check code low position	Check code high position
0x01	0x03	0x01 0xF8	0x00 0x02	0x44	0x06

Response frame:

Address code	Function code	Return valid bytes	Humidity value	Temperature value	Check code low position	Checksum high position
0x01	0x03	0x04	0x02 0x92	0xFF 0x9B	0x5A	0x3D

Humidity value:

0292 (hexadecimal) = 658=> Humidity value = 65.8%RH

Temperature value: When the temperature is lower than 0℃, upload in the form of complement

FF9B (hexadecimal) = -101=> Temperature value = -10.1°C

3.3, modify the current address

Inquiry frame: (modify the current address to 0x02)

Address code	Function code	Register address	Modify value	Checksum low position	Checksum high position
0x01	0x06	0x07 0xD0	0x00 0x02	0x08	0x86

Response frame:

Address code	Function code	Register address	Modify value	Check code low bit	Check code high bit
0x01	0x06	0x07 0xD0	0x00 0x02	0x08	0x86

3.4, Modify the current baud rate

Inquiry frame: (Modify the current baud rate to 9600)

Address code	Function code	Register address	Modify value	Check code low bit	Check code high
0x01	0x06	0x07 0xD1	0x00 0x02	0x59	0x46

Response frame:

Address code	Function code	Register address	Modify value	Check code low	Check code high
0x01	0x06	0x07 0xD1	0x00 0x02	0x59	0x46

3.5. Query current address and baud rate

Inquiry frame:

Address code	Function code	Register address	Data length	Check code low bit	Check code high bit
0xFF	0x03	0x07 0xD0	0x00 0x02	0xD1	0x58

Response frame:

Address code	Function code	Return valid bytes	Address	Baud rate	Check code low bit	Check code high bit
0x01	0x03	0x04	0x00 0x01	0x00 0x01	0x6A	0x33

The real address of the device is 01, and the baud rate is 0x01, that is, 4800.

Other Supplementary Information

Installation Instructions

When measuring wind speed and direction, the N-shaped direction on the weather station sensor should be installed facing due north to avoid errors.
The applicable range of the bottom mounting bar: 46-51mm

The following installation methods are recommended (the bracket needs to be purchased or built by yourself)