STM32 SPI usage and SPI initialization precautions

In the STM32F10x series chips, although the number of SPI synchronous serial ports is different, the initialization method is the same. When using SPI, we recall the use of GPIO and pay attention to 6 points. We will mainly explain one point here.

According to the system's requirements for different functions, it will be more complicated to initialize different functional peripherals, initialize GPIO, and initialize SPI synchronous serial port devices. All SIP synchronous serial ports of STM32F10x series chips are shared with GPIO. The initialization of SPI is divided into two major parts, namely the initialization of the I/O port used by SPI and the initialization of SPI functions. For the pins used by the SPI synchronous serial port, according to the direction of the data, set GPIO_Mode_IN_FLOATING or GPIO_Mode_AF_PP multiplexing push-free output. The other settings are the same as the GPIO pin settings.

The initialization method of the SPI synchronous serial port parameters will be shown in a later example.

When we use SPI, we must turn on the clock of the SPI synchronous serial port, so that the system can send and receive data from this opened synchronous serial port.

RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1,ENABLE);

Sending data in SPI is very simple. When the data byte to be sent is written into the transmit buffer, the transmission process begins. However, before trying to write to the transmit buffer, it is necessary to confirm whether the TXE flag is 1.

Similarly for the receiver, when the data transmission is completed, the data is also completed after the end. At the last sampling clock edge, the RXNE flag is set. The data word received in the shift register is transferred to the receive buffer. The RXNE bit is cleared when the SPI_DR register is set.

Therefore: when sending data, it is necessary to determine whether the previous data has been sent. Only when the data is sent completely can new data be sent.

For example: PA7 is used as the MOSI pin of SPI1 synchronous serial port, PA6 is used as the MISO pin of SPI1 synchronous serial port, PA5 is used as the SCK pin, and PA4 is used as the NSS chip select pin. Define the synchronous serial port SPI1 as the master device, send 8 data bits each time, the high bit is first, the SPI clock frequency is 9MHz, the data is captured at the second clock edge, the clock is low when idle, and the NSS pin is managed by software.

The complete code is as follows:

#include "stm32f10x_lib.h"

void SPI_Configuration(void)

{

// SPI_1 serial port parameter definition, SPI_1 parameters are clock is usually high, rising edge sampling

SPI_InitTypeDef SPI_InitStructure;

GPIO_InitTypeDef GPIO_InitStructure;

RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI2,ENABLE); //Enable SPI_2 clock

//Configure SPI1's MISO (PA6) as a floating input

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;

GPIO_InitStructure.GPIO_MODE = GPIO_Mode_IN_FLOATING;

GPIO_Init(GPIOA,&GPIO_InitStructure);

//Configure SPI1's MOSI (PA7) and SPI1's CLK (PA5) as multiplexed push-to-disconnect outputs

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5|GPIO_Pin_7;

GPIO_InitSturcture.GPIO_Speed ​​= GPIO_Speed_50MHz;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;

GPIO_Init(GPIOA,&GPIO_InitStructure);

//Configure SPI1's NSS (PA4) as push output

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;

GPIO_InitSturcture.GPIO_Speed ​​= GPIO_Speed_50MHz;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;

GPIO_Init(GPIOA,&GPIO_InitSturcture);

//SPI1 synchronization parameter initialization definition

SPI_InitTypeDef SPI_InitStructure;

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_Fullduplex;

SPI_InitStructure.SPI_Mode = SPI_Mode_Master;

SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;

SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;

SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;

SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;

SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_4;

SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_InitStructure.SPI_CRCPolynomial = 7;

SPI_Init(SPI1,&SPI_InitStructure);

SPI_Cmd(SPI1,ENABLE);

}

//Send a data through SPI1 port and receive a data at the same time

unsigned char SPI_SendByte(unsigned char Byte)

{

//If the register data is not sent, wait in a loop

while(SPI_T1S_GetFlagStatus(SPI1,SPI_T1S_FLAG_TXE) == RESET);

//Write the data to be sent to the send register

SPI_T1S_SendData(SPI2,Byte);

//If the receiving register does not receive data, loop

while(SPI_T1S_GetFlagStatus(SPI1,SPI_T1S_FLAG_RXNE) == RESET);

return SPI_T1S_ReceiveData(SPI1);

}