AD9850在DSP环境下的控制字程序实现：

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void dds_reset(void);        //DDS主复位程序
void dds_serialmode(void);    //DDS串行方式设置
void dds_set(void);            //DDS设置数据发送
void fre2word(void);        //DDS控制字计算
void freupdata(void);        //DDS频率输出更新
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//其他函数此处省略，只留下了表的结构和控制字计算部分……

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//控制字表，DDS＝9850，晶振＝16MHZ
    //word=0x100000000*fre/16000000;
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unsigned char code dds_word_10mhz[2][4]={
    0x00,0x00,0x00,0x00,
    0x00,0x00,0x00,0xa0
};

unsigned char code dds_word_1mhz[10][4]={
    0x00,0x00,0x00,0x00,
    0x00,0x00,0x00,0x10,
    0x00,0x00,0x00,0x20,
    0x00,0x00,0x00,0x30,
    0x00,0x00,0x00,0x40,
    0x00,0x00,0x00,0x50,
    0x00,0x00,0x00,0x60,
    0x00,0x00,0x00,0x70,
    0x00,0x00,0x00,0x80,
    0x00,0x00,0x00,0x90
};
unsigned char code dds_word_100khz[10][4]={
    0x00,0x00,0x00,0x00,            //0
    0x99,0x99,0x99,0x01,        //1
    0x33,0x33,0x33,0x03,        //2
    0xcc,0xcc,0xcc,0x04,        //3
    0x66,0x66,0x66,0x06,        //4
    0x00,0x00,0x00,0x08,        //5
    0x99,0x99,0x99,0x09,        //6
    0x33,0x33,0x33,0x0b,        //7
    0xcc,0xcc,0xcc,0x0c,        //8
    0x66,0x66,0x66,0x0e            //9
};
unsigned char code dds_word_10khz[10][4]={
    0x00,0x00,0x00,0x00,        //0
    0xc2,0xf5,0x28,0x00,        //1
    0x85,0xeb,0x51,0x00,        //2
    0x47,0xe1,0x7a,0x00,        //3
    0x0a,0xd7,0xa3,0x00,        //4
    0xcc,0xcc,0xcc,0x00,        //5
    0x8f,0xc2,0xf5,0x00,        //6
    0x51,0xb8,0x1e,0x01,        //7
    0x14,0xae,0x47,0x01,        //8
    0xd7,0xa3,0x70,0x01,        //9
};
unsigned char code dds_word_1khz[10][3]={
    0x00,0x00,0x00,        //0
    0x93,0x18,0x04,        //1
    0x26,0x31,0x08,        //2
    0xba,0x49,0x0c,        //3
    0x4d,0x62,0x10,        //4
    0xe1,0x7a,0x14,        //5
    0x74,0x93,0x18,        //6
    0x08,0xac,0x1c,        //7
    0x9b,0xc4,0x20,        //8
    0x2f,0xdd,0x24,        //9
};
unsigned char code dds_word_100hz[10][3]={
    0x00,0x00,0x00,        //0
    0xdb,0x68,0x00,        //1
    0xb7,0xd1,0x00,        //2
    0x92,0x3a,0x01,        //3
    0x6e,0xa3,0x01,        //4
    0x49,0x0c,0x02,        //5
    0x25,0x75,0x02,        //6
    0x00,0xde,0x02,        //7
    0xdc,0x46,0x03,        //8
    0xb7,0xaf,0x03        //9
};
unsigned char code dds_word_10hz[10][2]={
    0x00,0x00,        //0
    0x7c,0x0a,        //1
    0x14,0xf8,        //2
    0x75,0x1f,        //3
    0xf1,0x29,        //4
    0x6d,0x34,        //5
    0xea,0x3e,        //6
    0x66,0x49,        //7
    0xe2,0x53,        //8
    0x5f,0xfe        //9
};
unsigned char code dds_word_1hz[10][2]={
    0x00,0x00,        //0
    0x0c,0x01,        //1
    0x18,0x02,        //2
    0x25,0x03,        //3
    0x31,0x04,        //4
    0x3e,0x05,        //5
    0x4a,0x06,        //6
    0x57,0x07,        //7
    0x63,0x08,        //8
    0x6f,0x09        //9
};

/********************************************/

//控制字计算
void fre2word(void
){
    unsigned int temp1,temp2;
    
        //计算W0的值。注意，本例DDS工作在串行方式，这里W0是指控制字低8位，请区别于并行方式
    temp1=dds_word_1hz[fre[7]][0]+dds_word_10hz[fre[6]][0]+dds_word_100hz[fre[5]][0]+dds_word_1khz[fre[4]][0]+dds_word_10khz[fre[3]][0]+dds_word_100khz[fre[2]][0]+dds_word_1mhz[fre[1]][0]+dds_word_10mhz[fre[0]][0];
    W[0]=(unsigned char)temp1;
    //计算W0相加时的进位
    temp2=(unsigned char)(temp1>>8);

    //计算W1值
    temp1=dds_word_1hz[fre[7]][1]+dds_word_10hz[fre[6]][1]+dds_word_100hz[fre[5]][1]+dds_word_1khz[fre[4]][1]+dds_word_10khz[fre[3]][1]+dds_word_100khz[fre[2]][1]+dds_word_1mhz[fre[1]][1]+dds_word_10mhz[fre[0]][1]+temp2;
    W[1]=(unsigned char)temp1;
    temp2=(unsigned char)(temp1>>8);

    //计算W2值
    temp1=dds_word_100hz[fre[5]][2]+dds_word_1khz[fre[4]][2]+dds_word_10khz[fre[3]][2]+dds_word_100khz[fre[2]][2]+dds_word_1mhz[fre[1]][2]+dds_word_10mhz[fre[0]][2]+temp2;
    W[2]=(unsigned char)temp1;
    temp2=(unsigned char)(temp1>>8);

    //计算W3值
    temp1=dds_word_10khz[fre[3]][3]+dds_word_100khz[fre[2]][3]+dds_word_1mhz[fre[1]][3]+dds_word_10mhz[fre[0]][3]+temp2;
    W[3]=(unsigned char)temp1;
}