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This article mainly shows you the "STM32 serial port example analysis", the content is easy to understand, clear, hope to help you solve your doubts, the following let the editor lead you to study and learn "STM32 serial port example analysis" this article.

01. Characteristics of USART

USART is a general asynchronous transceiver (UniversalAsynchronousReceiver/Transmitter), usually called UART, which is a kind of asynchronous transceiver and the key module of asynchronous communication between devices. UART is responsible for handling the serial / parallel and parallel / serial conversion between the data bus and the serial port, and defines the frame format; as long as the two sides of the communication use the same frame format and baud rate, they can complete the communication process with only two signal lines (Rx and Tx) without sharing the clock signal, so it is also called asynchronous serial communication.

Full-duplex asynchronous communication.

The decimal baud rate generator system provides accurate baud rate.

Configurable 16x oversampling or 8x oversampling makes it possible to configure speed tolerance and clock tolerance flexibly.

Programmable data word length (8 or 9 bits)

Configurable stop bit (1 or 2 stop bits are supported)

Configurable communication using DMA multi-buffers.

Separate transmitter and receiver enable bits.

Detection flag: ① accept buffer ② send buffer empty ③ transmission end flag

Multiple marked interrupt sources. Trigger the interrupt.

Others: check control, four error detection flags.

Communication structure

02. Introduction to USART 2.1.data transfer model

1. Data packet

The data packet of serial communication is transmitted by the sending equipment to the RXD interface of the receiving device through its own TXD interface. The content of the data packet is specified in the protocol layer, including the starting bit, the main data (8 or 9 bits), the check bit and the stop bit. Both sides of the communication must agree on the format of the data packet in order to send and receive data normally.

two。 Baud rate

Because there is no clock signal in asynchronous communication, the receiver and receiver should agree on the baud rate, that is, the number of symbols transmitted per second, in order to decode the signal, the common baud rate is 4800, 9600, 115200 and so on. The setting of baud rate in STM32 is realized by initializing the structure of serial port.

3. Start and stop signals

The beginning and end of the data packet are the start bit and the stop bit, respectively. The start signal of the packet is represented by a logical 0 data bit, and the stop bit signal can be represented by 0.5, 1, 1.5, and 2 logical 1 data bits. The setting of start and stop signals in STM32 is also realized by serial port initialization structure.

4. Valid data

Valid data specifies the length of subject data, which is usually 8 or 9 bits, which is also realized through serial port initialization structure in STM32.

5. Data check

After the valid data, there is an optional data check bit. Because the data communication is relatively more vulnerable to external interference, the transmission data deviation can be solved by adding parity bits in the transmission process. The check methods are odd, even, space, mark and noparity. These can also be implemented in the serial initialization structure.

2.3, Baud rate

If the clock is 84m

USARTDIV = 84000000 / (1152000016) = 45.572

So get:

DIV_Fraction = 1600.572 = 0x09

DIV_Mantissa = 45 = 0x2D

03. USART of STM32

According to STM32F207 data manual, STM32F207 has a total of 6 serial ports

04. Code configuration

Configure interrupt priority.

/ * Enable the USARTx Interrupt * / NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn; NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1; NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0; NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; NVIC_Init (& NVIC_InitStructure)

Open the serial port and the corresponding GPIO pin, configure the corresponding serial port information and the working mode of the GPIO pin.

/ * Enable GPIO clock * / RCC_AHB1PeriphClockCmd (RCC_AHB1Periph_GPIOA, ENABLE); / * Enable UART1 clock * / RCC_APB2PeriphClockCmd (RCC_APB2Periph_USART1, ENABLE); / * Connect PXx to USARTx_Tx*/ GPIO_PinAFConfig (GPIOA, 9, GPIO_AF_USART1); / * Connect PXx to USARTx_Rx*/ GPIO_PinAFConfig (GPIOA, 10, GPIO_AF_USART1); / * Configure USART Tx as alternate function * / GPIO_InitStructure.GPIO_OType = GPIO_OType_PP GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init (GPIOA, & GPIO_InitStructure); / * Configure USART Rx as alternate function * / GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10; GPIO_Init (GPIOA, & GPIO_InitStructure)

Configure USART1.

USART_InitStructure.USART_BaudRate = 115200 USART_InitStructure.USART_Mode / configuration baud rate USART_InitStructure.USART_WordLength = USART_WordLength_8b;// configuration data word length USART_InitStructure.USART_StopBits = USART_StopBits_1;// configuration stop bit USART_InitStructure.USART_Parity = USART_Parity_No;// configuration parity bit USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;// configuration hardware flow control USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx / / configure the working mode, send and receive / * USART configuration * / USART_Init (USART1, & USART_InitStructure) together; / / complete the initialization configuration of the serial port

Enable to interrupt the configuration.

USART_ITConfig (USART1, USART_IT_TC, ENABLE); USART_ITConfig (USART1, USART_IT_RXNE, ENABLE)

We configure sending transmission completion interrupts and receiving data registers non-null interrupts. We can configure many types of interrupts, as you can see in the standard library functions provided by ST.

/ * * @ brief Enables or disables the specified USART interrupts. * @ param USARTx: where x can be 1,2,3,4,5 or 6 to select the USART or * UART peripheral. * @ param USART_IT: specifies the USART interrupt sources to be enabled or disabled. * This parameter can be one of the following values: * @ arg USART_IT_CTS: CTS change interrupt * @ arg USART_IT_LBD: LIN Break detection interrupt * @ arg USART_IT_TXE: Transmit Data Register empty interrupt * @ arg USART_IT_TC: Transmission complete interrupt * @ arg USART_IT_RXNE: Receive Data register not empty Interrupt * @ arg USART_IT_IDLE: Idle line detection interrupt * @ arg USART_IT_PE: Parity Error interrupt * @ arg USART_IT_ERR: Error interrupt (Frame error Noise error, overrun error) * @ param NewState: new state of the specified USARTx interrupts. * This parameter can be: ENABLE or DISABLE. * @ retval None * /

Finally, enable serial port.

/ * Enable USART * / USART_Cmd (USART1, ENABLE)

Main main function, the function is that LCD displays the 10 characters received by the serial port (not shown if it is not ascii code), and the serial port returns the received 10 bytes in reverse order.

Int main (void) {/ * omit some initialization codes * / while (1) {if (LCD_refresh_flg) {LCD_refresh_flg = 0; LCD_ShowString (0Magne16 received data); receive_num--; USART_SendData (USART1, receive_ data [receive _ num--]); send_flg = 1;}

Because interrupts are enabled, we also need to write interrupt functions.

Void USART1_IRQHandler (void) {if (USART_GetFlagStatus (USART1, USART_FLAG_TC)) {if (send_flg = = 1) {if (receive_num==0) {USART_SendData (USART1, receive_ data [receive _ num]); send_flg = 0; receive_flg = 1;} else {USART_SendData (USART1, receive_ data [receive _ num--]) }} USART_ClearFlag (USART1, USART_FLAG_TC);} if (USART_GetFlagStatus (USART1, USART_FLAG_RXNE)) {if ((receive_flg) & & (send_flg = = 0)) {receive_ data [receive _ num++] = USART_ReceiveData (USART1); if (receive_num==10) {receive_flg = 0; LCD_refresh_flg = 1 USART_ClearFlag (USART1, USART_FLAG_RXNE);}}

Download verification

The LCD display screen can display the received 10 characters, and the PC sends data at 100ms intervals, sends 977 packets and receives 977 packets in reply. The test demo is robust enough and there is no packet loss.

The above is all the contents of this article "sample Analysis of STM32 Serial Port". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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