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MODBUS protocol
Function code used by the product:
0x03: read holding register
0x04: Read input register
0x06: Write a single holding register
0x10: Write multiple holding registers
| Register type | Register address | Data content | Number of bytes |
| Input register | 0x0001 | Temperature value | 2 |
| 0x0002 | Humidity value | 2 | |
| Holding register | 0x0101 | Device address ( 1~247 ) | 2 |
| 0x0102 | Baud rate 0:9600 1:14400 2:19200 | 2 | |
| 0x0103 | Temperature correction value (/10) -10.0~10.0 | 2 | |
| 0x0104 | Humidity correction value (/10) -10.0~10.0 | 2 |
Modbus communication format :
The host sends a data frame:
| Slave address | function code | Register address High byte | Register address Low byte | Number of registers High byte | Number of registers Low byte | CRC High byte | CRC Low byte |
Slave response data frame:
| Slave address | Response function code | Number of bytes | Register1 data High byte | Register1 data Low byte | RegisterN data High byte | RegisterN data Low byte | CRC High byte | CRC Low byte |
MODBUS command frame
The host reads the temperature command frame (0x04) :
| Slave address | function code | Register address High byte | Register address Low byte | Number of registers High byte | Number of registers Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x04 | 0x00 | 0x01 | 0x00 | 0x01 | 0x60 | 0x0a |
Slave response data frame:
| Slave address | function code | Number of bytes | temperature High byte | temperature Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x04 | 0x02 | 0x01 | 0x31 | 0x79 | 0x74 |
Temperature value = 0x131, converted to decimal 305 , actual temperature value = 305 / 10 = 30.5 °C
NOTE: Symbol temperature is 16 hexadecimal, temperature = 0xFF33, converted to decimal -205 actual temperature = -20.5deg.] C;
The host reads the humidity command frame (0x04) :
| Slave address | function code | Register address High byte | Register address Low byte | Number of registers High byte | Number of registers Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x04 | 0x00 | 0x02 | 0x00 | 0x01 | 0xC1 | 0xCA |
Slave response data frame:
| Slave address | function code | Number of bytes | humidity High byte | humidity Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x04 | 0x02 | 0x02 | 0x22 | 0xD1 | 0xBA |
Humidity value = 0x222, converted to decimal 546 , actual humidity value = 546 / 10 = 54.6% ;
Continuous reading of the temperature and humidity command frame (0x04) :
| Slave address | function code | Register address High byte | Register address Low byte | Number of registers High byte | Number of registers Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x04 | 0x00 | 0x01 | 0x00 | 0x02 | 0x20 | 0x0B |
Slave response data frame:
| Slave address | function code | Number of bytes | temperature High byte | temperature Low byte | humidity High byte | humidity Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x04 | 0x04 | 0x01 | 0x31 | 0x02 | 0x22 | 0x2A | 0xCE |
Read the contents of the holding register (0x03) :
Take the slave address as an example:
| Slave address | function code | Register address High byte | Register address Low byte | Number of registers High byte | Number of registers Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x03 | 0x01 | 0x01 | 0x00 | 0x01 | 0xD4 | 0x0F |
Slave response frame:
| Slave address | function code | Number of bytes | Slave address High byte | Slave address Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x03 | 0x02 | 0x00 | 0x01 | 0x30 | 0x18 |
Modify the contents of the holding register (0x06) :
To modify the slave address as an example:
| Slave address | function code | Register address High byte | Register address Low byte | Register value High byte | Register value Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x06 | 0x01 | 0x01 | 0x00 | 0x08 | 0xD4 | 0x0F |
Modify slave address : 0x08 = 8
Slave response frame ( same as send ) :
| Slave address | function code | Register address High byte | Register address Low byte | Register value High byte | Register value Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x06 | 0x01 | 0x01 | 0x00 | 0x08 | 0xD4 | 0x0F |
Continuously modify the holding register (0x10) :
| Slave address | function code | initial address High byte | initial address Low byte | Number of registers High byte | Number of registers Low byte | Number of bytes | Register1 high byte | Register1 low byte | Register2 high byte | Register2 low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x06 | 0x01 | 0x01 | 0x00 | 0x02 | 0x04 | 0x00 | 0x20 | 0x25 | 0x80 | 0x25 | 0x09 |
Modify slave address : 0x20 = 32
Baud rate : 0x2580 = 9600
Slave response frame:
| Slave address | function code | Register address High byte | Register address Low byte | Number of registers High byte | Number of registers Low byte | CRC High byte | CRC Low byte |
| 0x01 | 0x06 | 0x00 | 0x11 | 0x00 | 0x04 | 0xD4 | 0x0F |
Normal version agreement
The baud rate defaults to 9600 (user can set it by itself), 8 -bit data, 1 bit stop, no parity
RS485 communication
| Serial command | Description |
| READ | Trigger a temperature and humidity report (27.4 °C , 67.7% temperature27.4 °C humidity 67.7%) |
| AUTO | Start the automatic temperature and humidity reporting function ( ibid. ) |
| STOP | Stop temperature and humidity automatic reporting |
| BR: XXXX | Set baud rate 9600~19200 (BR: 9600 baud rate is9600) |
| TC: XX.X | Set temperature calibration (-10.0~10.0) (TC: 02.0 temperature correction value is 2.0°C ) |
| HC: XX.X | Set humidity calibration (-10.0~10.0) (HC:-05.1 humidity correction value is-5.1%) |
| HZ: XXX | Set the temperature and humidity reporting rate (0.5,1,2,5,10) (HZ: 2 automatic reporting rate 2Hz) |
| PARAM | Read system current settings |
PARAM instruction :
TC: 0.0, HC: 0.0, BR: 9600, HZ: 1 -> Temperature correction value 0.0 Humidity correction value 0.0 Baud rate 9600Reporting rate 1 Hz
SLAVE_ADD: 1 -> MODBUS slave address 0x01
