stm32f4--serial port (USART) Communication summary

First, overview:

The Usart is a universal synchronous asynchronous transceiver for flexible full-duplex data exchange with external devices, which supports a variety of communication modes and provides multiple baud rates via the fractional baud rate generator.

Second, serial IO:

For stm32f407 there are 6 serial ports, for each serial port corresponding to the IO can be found from the chip schematic diagram, for its serial port 1, the corresponding IO for the PA9/PB6 port corresponding to the serial 1 transmitter, PA10/PB7 port corresponding to the serial 1 receiver.

Third, Communication parameters:

For data transmission needs to set up the relevant data transmission protocol, so the necessary parameter setting is necessary, including: Start bit, data bit (8 or 9 bits), parity bit (open or not), stop bit (1, 1.5, 2 bit), baud rate setting.

Iv. Related registers:

The relevant registers are: status register, data register, baud rate register, control register 1, Control register 2, control register 3, protection time and prescaler register; Below is a simple analysis of the first three registers.

1. Status Register:

The current known bits are: TXE: send register is empty; TC: Send complete; RXNE: Read data register is not empty; ORE: overflow error; FE: Frame error; PE: Parity error.

2, Data register: The register is only low 8 bits valid, and has read and write operations, the data in the register to send the data to be sent or the data received depends on whether the operation performed is read or write.

3. Baud Rate Register:

The baud rate register is used to generate the corresponding baud rate through the clock by setting the relevant values. The relationship between the numerical setting of the serial port 1 and the baud rate is as follows:

where the corresponding value is set in the register, div_mantissa[11,0] is used to set the integer part of the crossover factor, div_fraction[3,0] is used to set the fractional part of the divider factor.

V. Related Code Analysis:

Follow the configuration process of the serial port to analyze the relevant code:

1. Related clock enable:

Rcc_ahb1periphclockcmd (rcc_ahb1periph_gpioa,enable); Enable Gpioa clock Rcc_apb2periphclockcmd (rcc_apb2periph_usart1,enable);//enable USART1 clock

2. Pin multiplexing Mapping:

Serial 1 corresponds to pin multiplexing mapping gpio_pinafconfig (GPIOA,GPIO_PINSOURCE9,GPIO_AF_USART1); GPIOA9 Multiplexing is usart1gpio_pinafconfig (GPIOA,GPIO_PINSOURCE10,GPIO_AF_USART1); GPIOA10 Multiplexing for USART1

3. Gpio Port Mode setting:

USART1 port configuration        gpio_initstructure.gpio_pin = Gpio_pin_9 | gpio_pin_10; GPIOA9 and Gpioa10gpio_initstructure.gpio_mode = gpio_mode_af;//multiplexing function gpio_initstructure.gpio_speed = GPIO_Speed_50MHz ;//Speed 50mhzgpio_initstructure.gpio_otype = gpio_otype_pp; Push-pull multiplexing output gpio_initstructure.gpio_pupd = gpio_pupd_up; Pull-up gpio_init (gpioa,&gpio_initstructure); Initialize PA9,PA10

4. Serial Port parameter setting:

        USART1 initialization Setting Usart_initstructure.usart_baudrate = bound;//Baud rate setting Usart_initstructure.usart_wordlength = USART_ wordlength_8b;//Word length is 8-bit data format usart_initstructure.usart_stopbits = usart_stopbits_1;//a stop bit usart_initstructure.usart_ Parity = usart_parity_no;//no parity bit usart_initstructure.usart_hardwareflowcontrol = usart_hardwareflowcontrol_none;// No hardware data flow control Usart_initstructure.usart_mode = Usart_mode_rx | usart_mode_tx;//Transceiver Mode    usart_init (USART1, &usart_initstructure);//Initialize serial port 1

5. Configuration related interrupts:

#if en_usart1_rxusart_itconfig (USART1, Usart_it_rxne, enable);//Turn on related interrupts//usart1 NVIC configuration        nvic_initstructure.nvic_ Irqchannel = usart1_irqn;//Serial 1 interrupt channel nvic_initstructure.nvic_irqchannelpreemptionpriority=3;//preemption priority 3nvic_ Initstructure.nvic_irqchannelsubpriority =3;//Sub-priority 3nvic_initstructure.nvic_irqchannelcmd = ENABLE;//IRQ Channel Enable Nvic_ Init (&nvic_initstructure);//Initialize the VIC register, #endif according to the specified parameters

6, enable the serial port (and pay attention to the relevant flag bit):

        Usart_cmd (USART1, ENABLE);  Enable serial port 1 Usart_clearflag (USART1, USART_FLAG_TC);

7. Interrupt Service function (self-processing as required):

if (Usart_getitstatus (USART1, usart_it_rxne)! = RESET)  //Receive interrupt (Received data must be 0x0d 0x0a end) {Res =usart_receivedata ( USART1)///(USART1->DR);//Read received data if ((usart_rx_sta&0x8000) ==0)//Receive incomplete {if (usart_rx_sta&0x4000)// Received 0x0d{if (res!=0x0a) usart_rx_sta=0;//receive error, restart else usart_rx_sta|=0x8000;//receive completed}else//Not received 0x0d{if (res==0x0d) Usart_rx_sta|=0x4000;else{usart_rx_buf[usart_rx_sta&0x3fff]=res; Usart_rx_sta++;if (usart_rx_sta> (usart_rec_len-1)) usart_rx_sta=0;//receive data error, start receiving again}}}}      

8, the rest is based on the relevant transmission status of the serial port to send and receive data, according to their own needs for design and analysis.

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

stm32f4--serial port (USART) Communication summary