前言:
今天是2018蓝桥杯省赛的前一天,特此发表一篇以示纪念!
STM32 的TIM的捕获PWM波,是为了频率和占空比,这两种数据结果!它 的最基本的原理就是(打个比方):例如一个高电平上升沿过来,捕获的数值就是上升为的高电平的TIM的计数值(TIM定时器,CNT不断增加,再重新装载),这点是最基本的内容!后面就是通过前后的数值计算可以获得占空比 频率。
第一种方法:
官方的正统方法
IC1和IC2为一组通道,IC3和IC4为一组通道,以上图为例可以得到上升沿是IC1的值为600(假设),此时TIMx_CCR2不变,计数器复位为0,然后在下降沿的时候,IC2读取计数值 即为高电平时间300(假设),当道下一个周期的上升沿时,IC1读取为600,计数器复位为0;
void pwmIC_Init() { GPIO_InitTypeDef GPIO_InitStructure; NVIC_InitTypeDef NVIC_InitStructure; RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE); GPIO_InitStructure.GPIO_Pin = GPIO_Pin_7; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(GPIOA, &GPIO_InitStructure); TIM_ICInitStructure.TIM_Channel = TIM_Channel_2; TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising; TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI; TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1; TIM_ICInitStructure.TIM_ICFilter = 0x0; TIM_PWMIConfig(TIM3, &TIM_ICInitStructure); TIM_SelectInputTrigger(TIM3, TIM_TS_TI2FP2); TIM_SelectSlaveMode(TIM3, TIM_SlaveMode_Reset); TIM_SelectMasterSlaveMode(TIM3, TIM_MasterSlaveMode_Enable); TIM_Cmd(TIM3, ENABLE); TIM_ITConfig(TIM3, TIM_IT_CC2, ENABLE); NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn; NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0; NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1; NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; NVIC_Init(&NVIC_InitStructure); }
这里最关键的就是TIM_ICPolarity_Rising 为上升沿开始捕获,TIM_SelectInputTrigger(TIM3, TIM_TS_TI2FP2);
选择IC2为有效的输入端,就是IC2获得的就是周期了,而IC1就是在这里就是高电平的时间! 假设周期:600,高电平时间:300
选择IC2为有效的输入端,就是IC2获得的就是周期了,而IC1就是在这里就是高电平的时间! 假设周期:600,高电平时间:300
可以计算的得到占空比 = 300/600, 可以得到频率 =72M/ 600;
void TIM3_IRQHandler(void) { TIM_ClearITPendingBit(TIM3, TIM_IT_CC2); IC2Value = TIM_GetCapture2(TIM3); if (IC2Value != 0) { DutyCycle = (TIM_GetCapture1(TIM3) * 100) / IC2Value; Frequency = SystemCoreClock / IC2Value; } else { DutyCycle = 0; Frequency = 0; } }
以上就可以看出IC2为周期,IC1为高电平时间!
第二种方法:
第二种方法显得比较裸,采用的就只是获取前后两次上升沿中断的计数值差,来计算周期,从而计算频率!
void TIM_Cap_Init(u16 arr,u16 prc)//²¶»ñƵÂʳõʼ»¯ { //PA1 PA2 ¶¨Ê±Æ÷TIM2 ͨµÀ2 3 TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure; GPIO_InitTypeDef GPIO_InitStructure; TIM_ICInitTypeDef TIM_ICInitStructure; NVIC_InitTypeDef NVIC_InitStructure; RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE); RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA,ENABLE); GPIO_InitStructure.GPIO_Pin=GPIO_Pin_1 | GPIO_Pin_2; GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz; GPIO_InitStructure.GPIO_Mode=GPIO_Mode_IPU; GPIO_Init(GPIOA,&GPIO_InitStructure); GPIO_ResetBits(GPIOA,GPIO_Pin_1 | GPIO_Pin_2); NVIC_InitStructure.NVIC_IRQChannel=TIM2_IRQn; NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0; NVIC_InitStructure.NVIC_IRQChannelSubPriority=0; NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE; NVIC_Init(&NVIC_InitStructure); TIM_TimeBaseInitStructure.TIM_Prescaler=71; TIM_TimeBaseInitStructure.TIM_CounterMode=TIM_CounterMode_Up ; TIM_TimeBaseInitStructure.TIM_Period=arr; TIM_TimeBaseInitStructure.TIM_ClockDivision=TIM_CKD_DIV1; TIM_TimeBaseInit(TIM2,&TIM_TimeBaseInitStructure); TIM_ICInitStructure.TIM_Channel=TIM_Channel_2; TIM_ICInitStructure.TIM_ICPolarity=TIM_ICPolarity_Rising; TIM_ICInitStructure.TIM_ICSelection=TIM_ICSelection_DirectTI; TIM_ICInitStructure.TIM_ICPrescaler=TIM_ICPSC_DIV1; TIM_ICInitStructure.TIM_ICFilter=0x0; TIM_ICInit(TIM2,&TIM_ICInitStructure); TIM_ICInitStructure.TIM_Channel=TIM_Channel_3; TIM_ICInit(TIM2,&TIM_ICInitStructure); TIM_Cmd(TIM2,ENABLE); TIM_ITConfig(TIM2, TIM_IT_CC2 | TIM_IT_CC3,ENABLE); }
配置了IC2,和IC3来采集两路的周期值!
void TIM2_IRQHandler(void) { if(TIM_GetITStatus(TIM2,TIM_IT_CC2)==SET) { TIM_ClearITPendingBit(TIM2,TIM_IT_CC2); if(flag1==0) { one=TIM_GetCapture2(TIM2); flag1=1; } else if(flag1==1) { two=TIM_GetCapture2(TIM2); if(two>one) { value1=(two-one); } else { value1=((0xffff-one)+two); } Get_pinlv1=36000000/value1/36; flag1=0; } } if(TIM_GetITStatus(TIM2,TIM_IT_CC3)==SET) { TIM_ClearITPendingBit(TIM2,TIM_IT_CC3); if(flag2==0) { three=TIM_GetCapture3(TIM2); flag2=1; } else if(flag2==1) { four=TIM_GetCapture3(TIM2); if(four>three) { value2=(four-three); } else { value2=((0xffff-three)+four); } Get_pinlv2=36000000/value2/36; flag2=0; } } }
采用了点小操作,来计算前后两次上升沿的差!当然了,如果想要获取占空比的画,可以配置一个通道下降沿捕获,配合上升沿捕获即可,这里就不再示范了。
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