原子哥，
我计划生成一个频率为400Hz的pwm波，即周期应为2.5ms，我用的是TIM3的定时器，在初始化定时器模块时：预分频数为84-1，重装载数是2500-1，但实际用示波器观察pwm波的周期时为2.58ms，我心里想这与计算的偏差有点大，接近4%的误差，请问一下这个是正常的还是我设置出问题了。
用的是正点原子的开发。
部分代码如下
[mw_shl_code=c,true]//主函数部分
#include "drivers_usart.h"
#include "drivers_oled.h"
#include "drivers_keyboard.h"
#include "drivers_pwm.h"
bool view;
void Delay(__IO uint32_t nCount);
void Delay(__IO uint32_t nCount)
{
while(nCount--){}
}
int main(void)
{
TIM3_PWM_Init(2499,83);
while(1)
{
}//end of while(1)
}
//TIM3_PWM_Init函数
void TIM3_PWM_Init(u32 arr,u32 psc)
{
GPIO_InitTypeDef GPIO_InitStructure;
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE); //TIM3 时钟使能
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE); //使能porta时钟
GPIO_PinAFConfig(GPIOA,GPIO_PinSource6,GPIO_AF_TIM3); //GA6复用为TIM3
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6; //GPIOA6
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
GPIO_Init(GPIOA,&GPIO_InitStructure);
TIM_TimeBaseStructure.TIM_Prescaler=psc;
TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up;
TIM_TimeBaseStructure.TIM_Period=arr;
TIM_TimeBaseStructure.TIM_ClockDivision=TIM_CKD_DIV1;
TIM_TimeBaseInit(TIM3,&TIM_TimeBaseStructure);
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = 0xff;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init(TIM3, &TIM_OCInitStructure);
TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM3,ENABLE);
TIM_Cmd(TIM3, ENABLE);
}// end of void TIM14_PWM_Init(u32 arr,u32 psc)[/mw_shl_code]
[mw_shl_code=c,true]/************************* PLL Parameters *************************************/
#if defined (STM32F40_41xxx) || defined (STM32F427_437xx) || defined (STM32F429_439xx) || defined (STM32F401xx)
/* PLL_VCO = (HSE_VALUE or HSI_VALUE / PLL_M) * PLL_N */
#define PLL_M 8 //原来为25
#else /* STM32F411xE */
#if defined (USE_HSE_BYPASS)
#define PLL_M 8
#else /* STM32F411xE */
#define PLL_M 16
#endif /* USE_HSE_BYPASS */
#endif /* STM32F40_41xxx || STM32F427_437xx || STM32F429_439xx || STM32F401xx */ [/mw_shl_code]
[mw_shl_code=c,true]还有系统文件的HSE_VALUE已经设置为8000000.[/mw_shl_code]
[mw_shl_code=c,true]万分感谢！[/mw_shl_code]
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发表于 2015-10-20 11:42:13
发表于 2015-10-20 22:29:51
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