STM32标准库SPI的初始化

SPI的初始化比较简单，但是能明白原理是最好的，毕竟出了问题以后好排除。

SPI的初始化过程：

1、初始化GPIO

2、初始化SPI_InitStructure结构体

3、使能SPI外设

SPI的初始化结构体如下图所示：

typedef struct

{

  uint16_t SPI_Direction;          

  uint16_t SPI_Mode;                

  uint16_t SPI_Daize;            

  uint16_t SPI_CPOL;                

  uint16_t SPI_A;                

  uint16_t SPI_NSS;                

  uint16_t SPI_BaudRatePrescaler;  

  uint16_t SPI_FirstBit;            

  uint16_t SPI_CRCPolynomial;      

}SPI_InitTypeDef;

SPI_Direction为SPI的传输方向有如下选项：

#define SPI_Direction_2Lines_FullDuplex ((uint16_t)0x0000)     //2线全双工

#define SPI_Direction_2Lines_RxOnly     ((uint16_t)0x0400)      //2线只接收

#define SPI_Direction_1Line_Rx          ((uint16_t)0x8000)          //1线只接收

#define SPI_Direction_1Line_Tx          ((uint16_t)0xC000)          //1线只发送

#define IS_SPI_DIRECTION_MODE(MODE) (((MODE) == SPI_Direction_2Lines_FullDuplex) || \

                                     ((MODE) == SPI_Direction_2Lines_RxOnly) || \

                                     ((MODE) == SPI_Direction_1Line_Rx) || \

                                     ((MODE) == SPI_Direction_1Line_Tx))

SPI_Mode指定SPI的模式的可选择参数如下：

SPI主机模式下，主机输出SCK,从机时候接收SCK，当配置为主机模式接收数据的时候必须发送数据来启动SCK

#define SPI_Mode_ter                 ((uint16_t)0x0104)                       //主机模式

#define SPI_Mode_Slave                  ((uint16_t)0x0000)                        //从机模式

#define IS_SPI_MODE(MODE) (((MODE) == SPI_Mode_ter) || \

                           ((MODE) == SPI_Mode_Slave))

SPI_Daize为一帧数据的长度，可选参数为：

#define SPI_Daize_16b                ((uint16_t)0x0800)       //8位

#define SPI_Daize_8b                 ((uint16_t)0x0000)         //16位

#define IS_SPI_DAIZE(DAIZE) (((DAIZE) == SPI_Daize_16b) || \

                                   ((DAIZE) == SPI_Daize_8b))

一般选择为8位

SPI_CPOL和SPI_A是比较重要的参数，他们决定了触发信号和采样信号的时刻，

SPI_CPOL=0，SCK空闲状态为低电平

SPI_CPOL=1，SCK空闲状态为高电平

SPI_A=0，表示在第一个边沿跳变时采样

SPI_A=1，表示在第二个边沿跳变时采样

当SPI_CPOL=0，SPI_A=0时，SCK空闲状态为低电平，表示在第一个边沿跳变时采样，说明采样状态为上升沿采样，下降沿触发，

当SPI_CPOL=1，SPI_A=0时，SCK空闲状态为高电平，表示在第一个边沿跳变时采样，说明采样状态为下降沿采样，上升沿触发。

当SPI_CPOL=0，SPI_A=1时，SCK空闲状态为高电平，表示在第二个边沿跳变时采样，说明采样状态为下降沿，上升沿触发

当SPI_CPOL=1，SPI_A=1时，SCK空闲状态为高电平，表示在第二个边沿跳变时采样，说明采样状态为上升沿降沿，下降沿触发

特别提醒：这两个位必须和外设支持的传输方式一致

SPI_CPOL的可选择参数如下：

#define SPI_CPOL_Low                    ((uint16_t)0x0000)

#define SPI_CPOL_High                   ((uint16_t)0x0002)

#define IS_SPI_CPOL(CPOL) (((CPOL) == SPI_CPOL_Low) || \

                           ((CPOL) == SPI_CPOL_High))

SPI_A的可选择参数如下：

#define SPI_A_1Edge                  ((uint16_t)0x0000)

#define SPI_A_2Edge                  ((uint16_t)0x0001)

#define IS_SPI_A(A) (((A) == SPI_A_1Edge) || \

                           ((A) == SPI_A_2Edge))

SPI_NSS为CS信号线，该位表示CS信号是由软件模拟还是由硬件自动产生。官方推荐CS信号由软件模拟，毕竟CS信号比较简单。可选择的参数如下：

#define SPI_NSS_Soft                    ((uint16_t)0x0200)

#define SPI_NSS_Hard                    ((uint16_t)0x0000)

#define IS_SPI_NSS(NSS) (((NSS) == SPI_NSS_Soft) || \

                         ((NSS) == SPI_NSS_Hard))

/**

SPI_BaudRatePrescaler SPI的分频系数设置，可选参数如下

#define SPI_BaudRatePrescaler_2         ((uint16_t)0x0000)

#define SPI_BaudRatePrescaler_4         ((uint16_t)0x0008)

#define SPI_BaudRatePrescaler_8         ((uint16_t)0x0010)

#define SPI_BaudRatePrescaler_16        ((uint16_t)0x0018)

#define SPI_BaudRatePrescaler_32        ((uint16_t)0x0020)

#define SPI_BaudRatePrescaler_64        ((uint16_t)0x0028)

#define SPI_BaudRatePrescaler_128       ((uint16_t)0x0030)

#define SPI_BaudRatePrescaler_256       ((uint16_t)0x0038)

#define IS_SPI_BAUDRATE_PRESCALER(PRESCALER) (((PRESCALER) == SPI_BaudRatePrescaler_2) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_4) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_8) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_16) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_32) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_64) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_128) || \

                                              ((PRESCALER) == SPI_BaudRatePrescaler_256))

具体SPI的时钟可根据时钟树来设置。

SPI_FirstBit 表示先发送高位还是先发送低位

#define SPI_FirstBit_MSB                ((uint16_t)0x0000)

#define SPI_FirstBit_LSB                ((uint16_t)0x0080)

#define IS_SPI_FIRST_BIT(BIT) (((BIT) == SPI_FirstBit_MSB) || \

                               ((BIT) == SPI_FirstBit_LSB))

SPI_CRCPolynomial  为CRC值计算的多项式，参数可设置为任意数字

下面为SPI的初始化实例：

void SPI2_Init(void)

{

       GPIO_InitTypeDef GPIO_InitStructure;

       SPI_InitTypeDef  SPI_InitStructure;

RCC_APB2PerClockCmd( RCC_APB2Per_GPIOB, ENABLE );

RCC_APB1PerClockCmd( RCC_APB1Per_SPI2,  ENABLE );

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_13 | GPIO_Pin_14 | GPIO_Pin_15;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_Init(GPIOB, &GPIO_InitStructure);

  GPIO_SetBits(GPIOB,GPIO_Pin_13|GPIO_Pin_14|GPIO_Pin_15);  //PB13/14/15ÉÏÀ­

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;  

SPI_InitStructure.SPI_Mode = SPI_Mode_ter;

SPI_InitStructure.SPI_Daize = SPI_Daize_8b;

SPI_InitStructure.SPI_CPOL = SPI_CPOL_High;

SPI_InitStructure.SPI_A = SPI_A_2Edge;

SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;

SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_256;

SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_InitStructure.SPI_CRCPolynomial = 7;

SPI_Init(SPI2, &SPI_InitStructure);  

SPI_Cmd(SPI2, ENABLE); 

SPI2_ReadWriteByte(0xff);

}