ad5764的回讀，硬體spi介面

之前寫過了mcu通過硬體spi介面向dac芯片ad5764的資料暫存器寫值輸出電壓，ad5764的offset與gain暫存器的值也是可以通過硬體spi讀出來的，
第一步：將待讀取的芯片設定為讀模式

回讀的命令定義如下：

當要回讀時，應向輸入移位暫存器寫入0x010000，因為要將REG2、REG1、REG0全部設定為0，將A2、A1設定為0，將A0設定為1，同時將DB0設定為0；
第二步與第三步：

可以看到在時序圖中，回讀發生了2次資料發送（spi是同步通信，發送幾次意味著接收幾次），第一次發送向芯片寫入命令，告訴芯片準備讀哪個通道的哪個暫存器，回傳的資料是未定義的，可以不用管；第二次發送NOP，接收芯片回傳的暫存器的值，
接下來就是撰寫代碼實作功能了，因為板子上有2顆ad5762與2顆ad5764，還是需要使用徑訓鏈通信，
資料定義：

//REGISTER MAP
#define AD5764_NOP      0x000000
#define READ            0x800000
#define WRITE           0x000000
#define REG_FUNCTION    0x000000
#define REG_DATA        0x100000
#define REG_COARSE_GAIN 0x180000
#define REG_FINE_GAIN   0x200000
#define	REG_OFFSET      0x280000
#define DAC_A           0x000000
#define DAC_B           0x010000
#define DAC_C           0x020000
#define DAC_D           0x030000
#define DAC_ALL         0x040000
#define SDO_ENABLE      0x000000
#define SDO_DISABLE     0x000001

enum lcc_ch_num{
    ch1 = 1, ch2, ch3, ch4, ch5, ch6
};

enum lcc_ch_abcd{
    a = 1, b, c, d
};

typedef struct DAC_SEND_ARRAY
{
    uint32_t send_array[4];//AB
    uint32_t send_cd_array[4];//CD
    uint32_t receive_array[4];
}ad_5764_spi;

spi讀寫函式的實作程序，細講

//spi讀寫函式的實作程序在之前的博文中
void hw_spi_read_write(uint32_t *send_data, uint32_t *receice_data, uint8_t size)
{
    SPI_SET_SS0_LOW(SPI1);
    for (uint8_t i = 0; i < size; i++)
    {
        SPI_WRITE_TX0(SPI1, send_data[i]);
        SPI_TRIGGER(SPI1);
        while (SPI_IS_BUSY(SPI1));
        receice_data[i] = SPI_READ_RX0(SPI1);
    }
    SPI_SET_SS0_HIGH(SPI1);
    LDAC = PIN_LOW;
    Delay(1);
    LDAC = PIN_HIGH;
}

void daisy_chain_readregister(enum lcc_ch_num ch, enum lcc_ch_abcd abcd, uint32_t RegisterSelect)
{
    memset(spi_ad5764.send_array, 0, sizeof(spi_ad5764.send_array));
    // 設定ad5764為讀模式
    if (ch == ch1)
    {
        spi_ad5764.send_array[3] = 0x010000;
    }
    else if (ch == ch2)
    {
        spi_ad5764.send_array[2] = 0x010000;
    }
    else if (ch == ch3 || ch == ch4)
    {
        spi_ad5764.send_array[1] = 0x010000;
    }
    else if (ch == ch5 || ch == ch6)
    {
        spi_ad5764.send_array[0] = 0x010000;
    }
    hw_spi_read_write(spi_ad5764.send_array, spi_ad5764.receive_array, 4);
    switch (ch)
    {
    case ch1:
        if (abcd == a)
        {
            spi_ad5764.send_array[3] = READ + RegisterSelect + DAC_A;
        }
        else if (abcd == b)
        {
            spi_ad5764.send_array[3] = READ + RegisterSelect + DAC_B;
        }
        break;
    case ch2:
        if (abcd == a)
        {
            spi_ad5764.send_array[2] = READ + RegisterSelect + DAC_A;
        }
        else if (abcd == b)
        {
            spi_ad5764.send_array[2] = READ + RegisterSelect + DAC_B;
        }
        break;
    case ch3:
        if (abcd == a)
        {
            spi_ad5764.send_array[1] = READ + RegisterSelect + DAC_A;
        }
        else if (abcd == b)
        {
            spi_ad5764.send_array[1] = READ + RegisterSelect + DAC_B;
        }
        break;
    case ch4:
        if (abcd == c)
        {
            spi_ad5764.send_array[1] = READ + RegisterSelect + DAC_C;
        }
        else if (abcd == d)
        {
            spi_ad5764.send_array[1] = READ + RegisterSelect + DAC_D;
        }
        break;
    case ch5:
        if (abcd == a)
        {
            spi_ad5764.send_array[0] = READ + RegisterSelect + DAC_A;
        }
        else if (abcd == b)
        {
            spi_ad5764.send_array[0] = READ + RegisterSelect + DAC_B;
        }
        break;
    case ch6:
        if (abcd == c)
        {
            spi_ad5764.send_array[0] = READ + RegisterSelect + DAC_C;
        }
        else if (abcd == d)
        {
            spi_ad5764.send_array[0] = READ + RegisterSelect + DAC_D;
        }
        break;
    default:
        break;
    }
    //發送讀哪個暫存器和哪個通道
    hw_spi_read_write(spi_ad5764.send_array, spi_ad5764.receive_array, 4);
    memset(spi_ad5764.send_array, 0, sizeof(spi_ad5764.send_array));
    memset(spi_ad5764.receive_array, 0, sizeof(spi_ad5764.receive_array));
    for (uint8_t i = 0; i < 4; i++)
    {
        spi_ad5764.send_array[i] = AD5764_NOP;
    }
    //發送接收命令
    hw_spi_read_write(spi_ad5764.send_array, spi_ad5764.receive_array, 4);
}

至此回讀功能就實作了，在測驗程序中發現，在設定為讀模式回讀暫存器值之后，如果要向資料暫存器寫入值輸出電壓，直接使用寫命令即可，無需將芯片設定為寫模式；另外我使用NUC123SD4AN0的SPI1介面可以將時鐘設定為16MHz，寫命令是正常的，但是回讀的時候，每次都少了2個bit（第0位和第1位），當我把SPI的時鐘降低為8MHz時，回讀會少1個bit（第0位），當把時鐘降低為4MHz時，回讀的資料才正確無誤了，不知為何，