1.原理:
通过定时器每隔一段时间触发一次DAC转换,然后通过DMA发送正玄波码表值给DAC.
2.实现
代码如下所示(采用的是定时器2,DAC引脚是PA4)
#define HZ(x) (u16)(72000000/sizeof(Sine12bit)*2/x) //计算Hz
#define DAC_DHR12R1 0x40007408 //外设DAC通道1的基地址
u16 Sine12bit[256] = { //正弦波描点
2048, 2098, 2148, 2198, 2248, 2298, 2348, 2398, 2447, 2496,
2545, 2594, 2642, 2690, 2737, 2785, 2831, 2877, 2923, 2968,
3013, 3057, 3100, 3143, 3185, 3227, 3267, 3307, 3347, 3385,
3423, 3460, 3496, 3531, 3565, 3598, 3631, 3662, 3692, 3722,
3750, 3778, 3804, 3829, 3854, 3877, 3899, 3920, 3940, 3958,
3976, 3992, 4007, 4021, 4034, 4046, 4056, 4065, 4073, 4080,
4086, 4090, 4093, 4095, 4095, 4095, 4093, 4090, 4086, 4080,
4073, 4065, 4056, 4046, 4034, 4021, 4007, 3992, 3976, 3958,
3940, 3920, 3899, 3877, 3854, 3829, 3804, 3778, 3750, 3722,
3692, 3662, 3631, 3598, 3565, 3531, 3496, 3460, 3423, 3385,
3347, 3307, 3267, 3227, 3185, 3143, 3100, 3057, 3013, 2968,
2923, 2877, 2831, 2785, 2737, 2690, 2642, 2594, 2545, 2496,
2447, 2398, 2348, 2298, 2248, 2198, 2148, 2098, 2047, 1997,
1947, 1897, 1847, 1797, 1747, 1697, 1648, 1599, 1550, 1501,
1453, 1405, 1358, 1310, 1264, 1218, 1172, 1127, 1082, 1038,
995, 952, 910, 868, 828, 788, 748, 710, 672, 635,
599, 564, 530, 497, 464, 433, 403, 373, 345, 317,
291, 266, 241, 218, 196, 175, 155, 137, 119, 103,
88, 74, 61, 49, 39, 30, 22, 15, 9, 5,
2, 0, 0, 0, 2, 5, 9, 15, 22, 30,
39, 49, 61, 74, 88, 103, 119, 137, 155, 175,
196, 218, 241, 266, 291, 317, 345, 373, 403, 433,
464, 497, 530, 564, 599, 635, 672, 710, 748, 788,
828, 868, 910, 952, 995, 1038, 1082, 1127, 1172, 1218,
1264, 1310, 1358, 1405, 1453, 1501, 1550, 1599, 1648, 1697,
1747, 1797, 1847, 1897, 1947, 1997 };
/*************************************************************
Function : set_Sine12bit
Description : 设置正玄波码表
Input : MAX(正峰峰值) MIN(负峰峰值)
return : none
*************************************************************/
void Set_Sine12bit(float MAX,float MIN)
{
int i;
float jiaodu=0;
float MID=(MAX+MIN)/2.0; //中间峰值
if(MAX>3.3) MAX=3.3;
else if(MAX<=MIN) MIN=0;
for(i=0;i<256;i++)
{
jiaodu=i*0.0247369; //当i =127时,表示为180度,由于sin()是弧度制,所以需要转换
Sine12bit[i]= ((float)sin(jiaodu)*(MAX-MID)+MID)*1241.212; //1241.212是比例,等于4096/3.3
}
}
/*************************************************************
Function : Set_Period
Description : 设置频率hz
Input : value(需要设置的频率hz值)
return : none
*************************************************************/
void Set_Period(u32 value)
{
TIM_ARRPreloadConfig(TIM2,DISABLE);
TIM2->ARR=HZ(value); //更新预装载值
TIM_ARRPreloadConfig(TIM2,ENABLE);
}
/*************************************************************
Function : TIM2_Int_Init
Description: 初始化定时器2
Input : Hz (需要初始化的频率hz值)
return : none
*************************************************************/
void TIM2_Int_Init(u32 Hz)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);//初始化定时器2与6的时钟
TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
TIM_TimeBaseStructure.TIM_Period = HZ(Hz); //正弦波频率设置
TIM_TimeBaseStructure.TIM_Prescaler = 0x0; //没有预分频
TIM_TimeBaseStructure.TIM_ClockDivision = 0x0; //时钟不分频 72M
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; //增计数
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
TIM_SelectOutputTrigger(TIM2, TIM_TRGOSource_Update);//更新TIM2输出触发
}
/*************************************************************
Function : DAC_DMA_Config
Description: 初始化DAC和DMA
Input : none
return : none
*************************************************************/
void DAC_DMA_Config(void)
{
DAC_InitTypeDef DAC_InitStructure;
DMA_InitTypeDef DMA_InitStructure;
GPIO_InitTypeDef GPIO_InitStructure;
RCC_APB1PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_DAC, ENABLE);//初始化DAC的时钟
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_DMA2, ENABLE);//初始化DMA2的时钟
/*初始化GPIO*/
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4 ;//DAC channel1和channel2对应的引脚
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP; //推挽输出
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
/*初始化DAC寄存器*/
DAC_StructInit(&DAC_InitStructure);
DAC_InitStructure.DAC_Trigger = DAC_Trigger_T2_TRGO;//指定DAC1的触发定时器TIM2
DAC_InitStructure.DAC_WaveGeneration = DAC_WaveGeneration_None;//无波形产生
DAC_InitStructure.DAC_OutputBuffer = DAC_OutputBuffer_Enable; //不是能DAC输出缓冲
DAC_Init(DAC_Channel_1, &DAC_InitStructure);//初始化DAC channel1
DAC_Cmd(DAC_Channel_1, ENABLE); //使能DAC channel1
DAC_DMACmd(DAC_Channel_1, ENABLE); //使能DAC Channel1的DMA
/*初始化DMA寄存器*/
DMA_DeInit(DMA2_Channel3); //将DMA配置成默认值
DMA_InitStructure.DMA_PeripheralBaseAddr = DAC_DHR12R1;//指定DMA2通道3的目标地址为DAC1_DHR12R1
DMA_InitStructure.DMA_MemoryBaseAddr = (uint32_t)&Sine12bit;//指定DMA的源地址为数组Sine12bit
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralDST;//外设作为数据传输的目的地
DMA_InitStructure.DMA_BufferSize = sizeof(Sine12bit)/2;//DMA缓冲区大小
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;//外设机地址存器不变
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable; //内存地址寄存器递增
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;//外设数据宽度为半字
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;//内存数据宽度为半字
DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;//工作在循环缓存模式，数据传输数为0时，自动恢复配置初值
DMA_InitStructure.DMA_Priority = DMA_Priority_VeryHigh;//非常高优先级
DMA_InitStructure.DMA_M2M = DMA_M2M_Disable;//通道未被设置成内存到内存模式，与循环模式相对
DMA_Init(DMA2_Channel3, &DMA_InitStructure);//初始化DMA
DMA_Cmd(DMA2_Channel3, ENABLE); //使能DMA的channel3
TIM_Cmd(TIM2, ENABLE); //最后开启TIM2转换
}
然后在main()函数里,调用USART_handler()
其中USART_handler()函数实现如下:
void USART_handler()
{
u8 len;
u32 hz; //获取HZ频率
float dac_max,dac_min; //获取DAC峰值
if(USART_RX_STA&0x8000)
{
len=USART_RX_STA&0x2F;
USART_RX_BUF[len]=0;
sscanf((char *)USART_RX_BUF,"%d,%f,%f",&hz,&dac_max,&dac_min);
printf("SET HZ = %d, MAX = %f,MIN = %f\r\n", hz,dac_max,dac_min);
Set_Sine12bit(dac_max,dac_min); //更改峰值
Set_Period( hz); //更改频率
USART_RX_STA=0;
}
}
3.进入串口试验
1)设置频率=50hz,正峰值=3.3V,负峰值=0V,串口则发送50,3.3,0.0,如下图所示:
示波器测量:
2)设置频率=100hz,正峰值=3V,负峰值=0V, 串口则发送100,3,0.0:
3)设置频率=100hz,正峰值=2V,负峰值=1V, 串口则发送100,2,1:
4)设置频率=1khz,正峰值=3.3V,负峰值=0V, 串口则发送1000,3.3,0:
5)设置频率=20khz,正峰值=3.3V,负峰值=0V,串口则发送20000,3.3,0:
是不是很简单~