Uart protocol between raspberrypi and STM32

Protocol format

- Start 8bit    0000000

- Command  xxxxxxxx, 

- Data           xxxxxxxx xxxxxxxx

- Cheksum

- End 8bit     11111111

Command 8bit	Data 8bit	S/R	Description
1	0-100 (100%)	S	Left traction
2	0-100 (100%)	S	Right traction
3	0-100 (100%)	S	Mower motor
4	0-30 (3m)	R	Ultrasonic