Gas Sensor Transmitter
http://www.trueyes.co.kr October 2018 Rev. 1.0
TT300
3
The TT300 communicates with other devices over RS485 bus. MODBUS follows RS485 communication standard.
See, Table 4, for configuration of RS485 communication.
Table 3. Communication Configuration
Baud rate 9600 bps
Stop Bits 1 bit
Parity Check None
Data Length 8 bits
The details about request and response protocols are given in, Table 5. And this protocol is followed by RTU (Remote
Terminal Unit). Description of MODBUS Protocol is given in, Table 6.
Name Bytes Description
Slave ID 1 Set Device ID, through a rotary switch.
Function Code 1 Reading and Writing Request Code.
Starting Address 2 Starting address of data bytes.
Request Quantity 2 Number of sensors to be loaded with data.
Data Length 1 Number of data bytes.
Data[n] n Number of data bytes (n), sent by sensor. (Each device sends 2 data bytes)
CRC 2 Error checking according to CRC16 standard.
Table 5. MODBUS Protocol Byte Description
No. of Bytes 1 1 2 2 2
Tx Slave ID Function Code Starting Address Request Quantity CRC
Table 4. MODBUS Protocol
No. of Bytes 1 1 1 n 2
Rx Slave ID Function Code Data Length Data[n] CRC
See Picture1, This touch switch is for configuration of RS485 Slaves’ Device ID.
If you touch the switch for 5 seconds, you hear a beeping sound. You can see the ID
increase each time you touch again after you release your finger from the switch. After
setting the desired ID, press the switch again for 5 seconds. When you hear a beep, the ID
setting is completed.
Picture 1. Touch Switch
RS 485 Interface
Touch
switch
