STM32 USART usage notes

Finally, I can't help but complain about the students who translated the STM 32 function library manual. A lot of things were omitted in the middle, and they were very important things. . . . . My heart almost collapsed!!!

Now let's talk about the pitfalls of USART serial communication in STM 32 function library 3.5:

In some tutorials and Chinese manuals, the basic configuration source code of USART is as follows

1. USART_InitTypeDef USART_InitStructure;  

2. USART_InitStructure.USART_BaudRate = 9600;  

3. USART_InitStructure.USART_WordLength = USART_WordLength_8b;  

4. USART_InitStructure.USART_StopBits = USART_StopBits_1;  

5. USART_InitStructure.USART_Parity = USART_Parity_Odd;  

6. USART_InitStructure.USART_HardwareFlowControl =  

7. USART_HardwareFlowControl_RTS_CTS;  

8. USART_InitStructure.USART_Mode = USART_Mode_Tx | USART_Mode_Rx;  

9. USART_InitStructure.USART_Clock = USART_Clock_Disable;  

10. USART_InitStructure.USART_CPOL = USART_CPOL_High;  

11. USART_InitStructure.USART_CPHA = USART_CPHA_1Edge;  

12. USART_InitStructure.USART_LastBit = USART_LastBit_Enable;  

13. USART_Init(USART1, &USART_InitStructure);  

Only one structure variable is declared above: USART_InitTypeDef USART_InitStructure;

Then we compile and find that the compilation error is reported, and the following clock variables are not defined

1. USART_InitStructure.USART_Clock = USART_Clock_Disable;  

2. USART_InitStructure.USART_CPOL = USART_CPOL_High;  

3. USART_InitStructure.USART_CPHA = USART_CPHA_1Edge;  

4. USART_InitStructure.USART_LastBit = USART_LastBit_Enable;  

Why is this? I clearly wrote it according to what the manual says 55555. . . .

As a last resort, I had to use our great Baidu to find out. Through some information and posts from netizens, I finally found the reason. It turned out that in version 3.5 of the function library, when initializing the USART default value, there is not only one structure variable USART_InitStructure, but also a structure variable for USART clock management:

USART_ClockInitTypeDef USART_ClockInitStructure;

So the final USART configuration function is:

1.        USART_InitTypeDef USART_InitStructure;     

2. USART_ClockInitTypeDef USART_ClockInitStructure;  

3. /*Baud rate 9600 8-bit data length 1 stop bit no parity bit 

4.   Disable hardware flow control Disable USART clock Clock polarity low Capture data on second edge 

5.   The clock pulse of the last bit of clock data is not output from SCLK*/  

6. USART_InitStructure.USART_BaudRate =9600;  

7. USART_InitStructure.USART_WordLength = USART_WordLength_8b;  

8. USART_InitStructure.USART_StopBits = USART_StopBits_1;  

9. USART_InitStructure.USART_Parity = USART_Parity_No;  

10. USART_InitStructure.USART_HardwareFlowControl =USART_HardwareFlowControl_None;  

11. USART_InitStructure.USART_Mode = USART_Mode_Tx | USART_Mode_Rx;  

12. USART_ClockInitStructure.USART_Clock = USART_Clock_Disable;  

13. USART_ClockInitStructure.USART_CPOL = USART_CPOL_High;  

14. USART_ClockInitStructure.USART_CPHA = USART_CPHA_2Edge;  

15. USART_ClockInitStructure.USART_LastBit = USART_LastBit_Disable;  

16. USART_Init(USART1, &USART_InitStructure);  

17. USART_ClockInit(USART1 , &USART_ClockInitStructure);  

1. Of course, don't forget to enable USART: USART_Cmd(USART1, ENABLE); and turn on the clock of the corresponding USART.  

1. Compile again and you will find that the compilation is correct, but this does not mean that you can use USART to send a "Hello World" to your computer. Continue down. Since almost all IO ports of STM32 are multiplexed, that is to say, an IO port is not only a regular input and output, it can also be used as an interface for on-chip peripherals such as USART/IIC/ADC. So when you use USART, you are actually sending and receiving data through the IO port. At this time, we also need to configure the corresponding IO port. Take USART1 as an example. Generally, it is multiplexed with ports 9 and 10 in GPIOA. If you are not sure, you can check the official manual of STM32, where GPIOA.9 is the data transmission port, i.e. TXD, and GPIOA.10 is the data receiving port RXD. Then we can configure it. The specific source code is as follows:  

1.                GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;             

2.     GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; //Note!! There is a very important point here, because USART is multiplexing port GPIOA.9, it is not a normal OUT but multiplexing AF  

3.     GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  

4.     GPIO_Init(GPIOA, &GPIO_InitStructure);  

5.   

6.     GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;             

7.     GPIO_InitStructure.GPIO_Mode =  GPIO_Mode_IN_FLOATING;    

8.     GPIO_Init(GPIOA, &GPIO_InitStructure);  

Well, now we have completed all the configurations of USART. Can't wait to send a message to PC through the development board? By using two functions
USART_ SendData and USART_ ReceiveData in the main function, we can realize the two-way communication between the development board and PC~~