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Notes
1.
To avoid damages, please confirm the polarity and the rated power supply before powering ON transmitter.
2.
To connect to the computer, user cannot directly use the RS connection. User needs to turn the RS level to the TTL level. Otherwise, the read
data will be out of order or garbled.
3.
If user don't know the address of the transmitter, they cannot read it on the RS485 network. User can only read the address in the stand-alone
state, modify it, and then connect it to the RS485 network.
4.
Kindly refer below instructions for MODBUS RS485 protocol.
MODBUS Protocol
Serial baud rate: 9600 8 N 1, Baud rate: 9600
Communication mode: RS485 transmission. Modbus RTU protocol, CRC check mode (low in front)
Serial return data time: <300ms
Read speed: <500ms
This protocol has the following functions: address reading, address modification and data reading.
Address read command：XX 00 XX XX 00 01 + Check (This feature cannot be read online)
XX
00
Address (any)
Function
Address read return: XX 00 02 00 xx + Check (xx indicates to be determined)
XX
Address (same as sending the first)
Modify the address command: (In advance through the above command to read the module current address is xx)
xx 01 00 yy 00 00 + Check (This feature cannot be read online)
xx
01
Current address
Function code
Current address: Read the module address with the address read command above. Default address is 02.
Function Code 01: 01 is the modify address command
Change address: Select a value from 2~255 (1 is reserved)
Address modification return: yy 01 02 00 yy + Check
yy
01
Modified address
Function code
Modified address: The above pre modification address, to determine the success of the address changes.
Part read data command : yy 03 00 03 00 01 + Check
yy
03
Address
Function code
Return data: yy 03 NN*2 xx xx......xx xx + Check
yy
03
Address
Function code
Calculation method: CO
_H * 256 + CO
2
Unit : ppm
XX
XX
Start address register (any)
00
02
Function
Data length
00
yy
Retain
Default address
02
Data length
Retain
00
03
Start address register
02
xx xx
Data length
CO2_H
_L
2
3
00
01
Read data byte length
00
xx
Retain
Address
00
00
Retain
Retain
00
yy
Modified address
00
01
Data length
xx xx
CO2_L
CRC check
CRC_L
CRC_H
CRC check
CRC_L
CRC_H
CRC check
CRC_L
CRC_H
CRC check
CRC_L
CRC_H
CRC check
CRC_L
CRC_H
CRC check
CRC_L
CRC_H
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