3
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 XX XX 00 01 CRC check
Address (any) Function Start address register (any) Read data byte length CRC_L CRC_H
Address read return: XX 00 02 00 xx + Check (xx indicates to be determined)
XX 00 02 00 xx CRC check
Address (same as sending the first) Function Data length Retain Address CRC_L CRC_H
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 00 yy 00 00 CRC check
Current address Function code Retain Default address Retain Retain CRC_L CRC_H
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 02 00 yy CRC check
Modified address Function code Data length Retain Modified address CRC_L CRC_H
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 00 03 00 01 CRC check
Address Function code Start address register Data length CRC_L CRC_H
Return data: yy 03 NN*2 xx xx……xx xx + Check
yy 03 02 xx xx xx xx CRC check
Address Function code Data length CO2_H CO2_L CRC_L CRC_H
Calculation method: CO2_H * 256 + CO2_L
Unit : ppm
