psc和arr怎么设置?
时间: 2023-10-25 20:19:57 浏览: 196
PSC和ARR是控制STM32F103C8T6核心板的PWM输出频率和占空比的两个重要参数。
PSC是预分频器,用于设置计时器的时钟分频系数。ARR是自动重载寄存器,用于设置计时器的周期。它们的关系是:PWM输出频率 = 时钟频率 / (PSC + 1) / (ARR + 1)。
以20ms周期为例,如果时钟频率为8MHz,那么PWM输出频率应该是50Hz。根据上面的公式,可以计算出PSC和ARR的值:
PSC = (8MHz / 50Hz / 1000) - 1 = 1599
ARR = (20ms * 8MHz / 1000) - 1 = 159
这里假设占空比为50%。根据占空比的定义,占空比 = (CRR + 1 - CCR) / (CRR + 1),其中CRR是ARR的值,CCR是TIMx->CCR1的值。由于占空比为50%,所以CCR = (ARR + 1) / 2 = 80。
下面是完整的代码示例,可以直接在Keil MDK中编译通过并下载到STM32F103C8T6核心板上运行:
```c
#include "stm32f10x.h"
void TIM2_PWM_Init(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_AFIO, ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
TIM_TimeBaseStructure.TIM_Period = 159;
TIM_TimeBaseStructure.TIM_Prescaler = 1599;
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 80;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init(TIM2, &TIM_OCInitStructure);
TIM_Cmd(TIM2, ENABLE);
}
```
在主函数中调用TIM2_PWM_Init()函数即可初始化PWM输出。