Reference

Library

URM_RS485 library on github

Communication Protocol Description

Default Information:

• Default Baudrate: 19200,8,N,1
• Default Address: 0x11
• Communication Command Format

Communication Commands and Returns frame Format:

PS: The sum byte value is the sum of all the byte value before. Just keep one byte from the total sum value.

Measure Distance

You could send a measure command to the Ultrasonic module. It will measure the distance, and send the value back through UART port.

For example:

Send Command: 0x55 0xAA 0x11 0x00 0x02 0x12

Instruction：

• Header----------------0x55
• Header----------------0xAA
• Address---------------0x11
• Length-----------------0x00
• Read Distance-------0x02
• Check Sum-----------0x12

Return Command：0x55 0xAA 0x11 0x02 0x02 0x12 0x34 0x5A

High 8-bit: 0x12;

Low 8-bit: 0x34

So the distance value is “0x1234”, which convert to decimal is 4660mm.

“0x5A” is low 8-bit of the check sum.

Measure Temperature

You could send a measure command to the Ultrasonic module. It will measure the temperature, and send the value back through UART port.

For example:

Send Command: 0x55 0xAA 0x11 0x00 0x03 0x13

Instruction：

• Header-----------------------0x55
• Header-----------------------0xAA
• Address-----------------------0x11
• Length------------------------0x00
• Read Temperature----------0x03
• Check Sum-------------------0x13

Return Command：0x55 0xAA 0x11 0x02 0x03 0x00 0xFF 0x14

High 8-bit: 0x00;

Low 8-bit: 0xFF

The output value will be “0x00FF”, which convert to decimal is 255. As the real temperature is 10% of the output value, so it is 25.5℃.

NOTE:

The measuring range is -10 to 70℃, it is a 16-signed integer. Negative digits are stored in two's complement' as in bitwise complement(~2). The method is judging whether BIT15 is “1”. If it is “1”, it means it is a negative number, the data will be inverted, and “1” should be added to the result.

Further information: https://www.arduino.cc/reference/en/language/structure/bitwise-operators/bitwisenot/

Set Address Command

The module default address is “0x11”. And the broadcast address is “0xAB”. If you don’t know the current address, but you want to set its address, you could use broadcast address to set the target address.

For example:

Send Command: 0x55 0xAA 0xAB 0x01 0x55 0x11 0x11

Instruction：

• Header-----------------------0x55
• Header-----------------------0xAA
• Broadcast Address---------0xAB
• Length------------------------0x01
• Address Setting CMD-----0x55
• Target Address---------------0x11
• Check Sum--------------------0x11

Return Command：0x55 0xAA 0x11 0x01 0x55 0xCC 0x32

The address of each device can be changed when multiple devices are connected. The new address must be between “0x11” and “0x80”. If you change it successfully, the module will return “0xCC”. If you fail, it will return “0xEE”.

Set the Detecting Range of the Ultrasonic Module

You could set the detecting range through UART interface. The proper range will increase sonar frequency and improve its accuracy.

For example:

If the module address is “0x11”, the range limit is 3840mm

Send Command: 0x55 0xAA 0x11 0x02 0x04 0x0F 0x00 0x25 //3840=0xF00

Instruction：

• Header-----------------------0x55
• Header-----------------------0xAA
• Address-----------------------0x11
• Length------------------------0x02
• Set Value CMD--------------0x04
• High 8-bit---------------------0x0F
• Low 8-bit----------------------0x00
• Check Sum--------------------0x25

Return Command: 0x55 0xAA 0x11 0x00 0x04 0xCC 0xE0

If you change it successfully, the module will return “0xCC”. If you fail, it will return “0xEE”.

Note: the default setting is the maximum value.

Read the Detecting Range of the Ultrasonic Module

You could read the detecting range through UART interface.

For example:

If the module address is “0x11”.

Send Command: 0x55 0xAA 0x11 0x00 0x05 0x15

Instruction：

• Header-----------------------0x55
• Header-----------------------0xAA
• Address----------------------0x11t
• Length-----------------------0x00
• Read value CMD---------------0x05
• Check Sum-------------------0x15

Return Command：0x55 0xAA 0x11 0x02 0x05 0x0F 0x00 0x26

So the return value is “0x0F00”, which convert to decimal is 3840mm

The unit of the distance is “mm”.

Set the UART Baudrate of the Ultrasonic Module

You could set communication baudrate of the ultrasonic module through UART interface.

For example:

If the module address is “0x11”.

Send Command: 0x55 0xAA 0x11 0x01 0x08 0x05 0x1E //set baudrate to 19200BPS

Instruction：

• Header-----------------------0x55
• Header-----------------------0xAA
• Address----------------------0x11
• Length------------------------0x01
• Baudrate Setting CMD---------0x08
• Target baudrate--------------0x05
• Check Sum--------------------0x1E

Return Command：0x55 0xAA 0x11 0x01 0x08 0xCC 0xE4

If you change it successfully, the module will return “0xCC”. If you fail, it will return “0xEE”.

Baudrate List:

document

Selection Guide