SPI的初始化比較簡單，但是能明白原理是最好的，畢竟出了問題以后好排除。

SPI的初始化過程：

1、初始化GPIO

2、初始化SPI_InitStructure結構體

3、使能SPI外設

SPI的初始化結構體如下圖所示：

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為SPI的傳輸方向有如下選項：

#define SPI_Direction_2Lines_FullDuplex ((uint16_t)0x0000)     //2線全雙工

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

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

#define SPI_Direction_1Line_Tx          ((uint16_t)0xC000)          //1線只發(fā)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的模式的可選擇參數(shù)如下：

SPI主機模式下，主機輸出SCK,從機時候接收SCK，當配置為主機模式接收數(shù)據(jù)的時候必須發(fā)送數(shù)據(jù)來啟動SCK

#define SPI_Mode_ter                 ((uint16_t)0x0104)                       //主機模式

#define SPI_Mode_Slave                  ((uint16_t)0x0000)                        //從機模式

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

                           ((MODE) == SPI_Mode_Slave))

SPI_Daize為一幀數(shù)據(jù)的長度，可選參數(shù)為：

#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))

一般選擇為8位

SPI_CPOL和SPI_A是比較重要的參數(shù)，他們決定了觸發(fā)信號和采樣信號的時刻，

SPI_CPOL=0，SCK空閑狀態(tài)為低電平

SPI_CPOL=1，SCK空閑狀態(tài)為高電平

SPI_A=0，表示在第一個邊沿跳變時采樣

SPI_A=1，表示在第二個邊沿跳變時采樣

當SPI_CPOL=0，SPI_A=0時，SCK空閑狀態(tài)為低電平，表示在第一個邊沿跳變時采樣，說明采樣狀態(tài)為上升沿采樣，下降沿觸發(fā)，

當SPI_CPOL=1，SPI_A=0時，SCK空閑狀態(tài)為高電平，表示在第一個邊沿跳變時采樣，說明采樣狀態(tài)為下降沿采樣，上升沿觸發(fā)。

當SPI_CPOL=0，SPI_A=1時，SCK空閑狀態(tài)為高電平，表示在第二個邊沿跳變時采樣，說明采樣狀態(tài)為下降沿，上升沿觸發(fā)

當SPI_CPOL=1，SPI_A=1時，SCK空閑狀態(tài)為高電平，表示在第二個邊沿跳變時采樣，說明采樣狀態(tài)為上升沿降沿，下降沿觸發(fā)

特別提醒：這兩個位必須和外設支持的傳輸方式一致

SPI_CPOL的可選擇參數(shù)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的可選擇參數(shù)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為CS信號線，該位表示CS信號是由軟件模擬還是由硬件自動產(chǎn)生。官方推薦CS信號由軟件模擬，畢竟CS信號比較簡單。可選擇的參數(shù)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的分頻系數(shù)設置，可選參數(shù)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))

具體SPI的時鐘可根據(jù)時鐘樹來設置。

SPI_FirstBit 表示先發(fā)送高位還是先發(fā)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  為CRC值計算的多項式，參數(shù)可設置為任意數(shù)字

下面為SPI的初始化實例：

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);  //PB13/14/15é?à-

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);

}