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DYACON UA-1 Manual Modbus
5.4 Modbus Protocol
Dyacon UA wind sensor uses the Modbus RTU format. The following are the protocol details
required for embedded devices to communicate with the Modbus sensor.
Notes:
•
Modbus data uses “big-endian” data format, 0x1234 is sent as 0x12 then 0x34.
•
The CRC uses “little-endian” data format, 0x1234 is sent as 0x34 then 0x12.
• The idle time between frames must be greater than or equal to 3.5 characters. The frame
inter character delay must be less than 1.5 characters.
•
The PDU Registers are addressed starting at zero. Therefore a register numbered as 201 is
addressed as 200.
The following is an example of a multi-register read of the air temperature, humidity, and
pressure starting at register number 202.
Detailed protocol information is available at www.modbus.org.
Request Frame
The following is an example of a read of the wind speed and wind direction with one request.
Field Name Length
(bytes)
Function Example
Data
Slave Address 1 Device address. 0x01
Function 1 Read holding register. 0x03
Register Start Address 2 Sensor address (201). 0x00C9
Quantity of Registers 2 Number of 16-bit registers to read. 0x0002
CRC 2 Error check. 0x3514
TX String (0x): 01 03 00 C9 00 02 14 35
Response Frame
Field Name Length
(bytes)
Function Example
Data
Slave Address 1 Device address. 0x01
Function 1 Read holding register. 0x03
Byte Count 1 Number (N) of data bytes. 0x04
Register Data N Register data, upper byte first.
Register 202 (Speed): 72 (7.2 m/s)
Register 203 (Direction): 3472 (347.2°)
0x0048
0x0D90
CRC 2 Error check. 0xD965
RX String: 01 03 04 00 48 0D 90 65 D9
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