Basic knowledge of communication interface

There are two ways for the processor to communicate with external devices

Parallel communication

Transmission principle ： All bits are transmitted at the same time

advantage ： Fast

shortcoming ： It takes up a lot of pin resources

Parallel communication

Transmission principle ： Data bits are transmitted in sequence

advantage ： Less pin resources

shortcoming ： Slow speed

stm32 Communication is mainly serial communication

serial communication

Simplex ： Only data can be transmitted in one direction

Half duplex ： Allows data to be transmitted in both directions , But it can only be transmitted in one direction at the same time

full duplex ： Allows data to be transmitted in both directions at the same time , It's actually a combination of two single duplex , Therefore, the sending and receiving equipment needs to have independent sending and receiving capabilities

communication mode

Synchronous communication ： With clock synchronous signal transmission

asynchronous communication ： No clock synchronization signal transmission

Commonly used serial communication interface

UART：TXD The sender ,RXD The receiver ,GND Common land , asynchronous communication , Full duplex

stm32f4 Communication interface

UART： Universal asynchronous transceiver

USART： Universal synchronous asynchronous transceiver

UART Asynchronous communication connection method

 

Communication corresponding pin

Serial number	RXD	TXD
1	PA10(PB7)	PA9（PB6)
2	PA3(PD6)	PA2(PD5)
3	PB11(PC11/PD9)	PB10(PC10/PD8)
4	PC11(PA1)	PC10(PA0)
5	PD2	PC12
6	PC7(PG9)	PC6(PG14)

stm32 Serial communication process

Data receiving process ： The external device serially inputs the data into the shift register , The speed is controlled by the agreed baud rate , After the data is completely entered , After entering the buffer register, the data enters the kernel .

Data transmission process ： The kernel enters the serial shift register through the buffer register , Send to external devices .

stm32 Parameters to be defined for serial asynchronous communication

1, example ： High level when not communicating 1, When low level is detected 0 when , Explain that the communication starts .

2, Data bits ：8 Bit or 9 position , One extra bit is parity bit . 

Odd check ： If the first eight bits of data are high 1 The number of is odd , repair 0, Is an even number of complements 1.

Even check ： If the first eight bits of data are high 1 The number of is odd , repair 1, Is an even number of complements 0.

3, Stop bit ： Last

4, Baud rate ： Both parties agree at the same time .