各位大神，求助以下，困了好多天了，自己做的最小系统板，在做PWM输出实验时，采用ST官方例程，输出的PWM波形恒定为250us左右，无论修改什么值都不引起周期变化。占空比的更改只在第一次用官方例程的时候那四个值有用，如果换成自己的选的值则完全没有效果。
[mw_shl_code=c,true]#include "stm32f10x.h"
#include "stm32f10x_it.h"
#include "stm32f10x_conf.h"
#include "delay.h"
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_OCInitTypeDef TIM_OCInitStructure;
uint16_t CCR1_Val = 333;
uint16_t PrescalerValue = 0;
/* Private function prototypes -----------------------------------------------*/
void RCC_Configuration(void);
void GPIO_Configuration(void);
int main(void)
{
/*!< At this stage the microcontroller clock setting is already configured,
this is done through SystemInit() function which is called from startup
file (startup_stm32f10x_xx.s) before to branch to application main.
To reconfigure the default setting of SystemInit() function, refer to
system_stm32f10x.c file
*/
/* System Clocks Configuration */
RCC_Configuration();
/* GPIO Configuration */
GPIO_Configuration();
/* -----------------------------------------------------------------------
TIM3 Configuration: generate 4 PWM signals with 4 different duty cycles:
The TIM3CLK frequency is set to SystemCoreClock (Hz), to get TIM3 counter
clock at 24 MHz the Prescaler is computed as following:
- Prescaler = (TIM3CLK / TIM3 counter clock) - 1
SystemCoreClock is set to 72 MHz for Low-density, Medium-density, High-density
and Connectivity line devices and to 24 MHz for Low-Density Value line and
Medium-Density Value line devices
The TIM3 is running at 36 KHz: TIM3 Frequency = TIM3 counter clock/(ARR + 1)
= 24 MHz / 666 = 36 KHz
TIM3 Channel1 duty cycle = (TIM3_CCR1/ TIM3_ARR)* 100 = 50%
TIM3 Channel2 duty cycle = (TIM3_CCR2/ TIM3_ARR)* 100 = 37.5%
TIM3 Channel3 duty cycle = (TIM3_CCR3/ TIM3_ARR)* 100 = 25%
TIM3 Channel4 duty cycle = (TIM3_CCR4/ TIM3_ARR)* 100 = 12.5%
----------------------------------------------------------------------- */
/* Compute the prescaler value */
PrescalerValue = 2;
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 665;
TIM_TimeBaseStructure.TIM_Prescaler = PrescalerValue;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* PWM1 Mode configuration: Channel1 */
TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
TIM_OCInitStructure.TIM_Pulse = CCR1_Val;
TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
TIM_OC1Init(TIM3, &TIM_OCInitStructure);
TIM_OC1PreloadConfig(TIM3, TIM_OCPreload_Enable);
TIM_ARRPreloadConfig(TIM3, ENABLE);
/* TIM3 enable counter */
TIM_Cmd(TIM3, ENABLE);
while (1)
{}
}
/**
* @brief Configures the different system clocks.
* @param None
* @retval None
*/
void RCC_Configuration(void)
{
/* TIM3 clock enable */
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
/* GPIOA and GPIOB clock enable */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA | RCC_APB2Periph_GPIOB |
RCC_APB2Periph_GPIOC | RCC_APB2Periph_AFIO, ENABLE);
}
/**
* @brief Configure the TIM3 Ouput Channels.
* @param None
* @retval None
*/
void GPIO_Configuration(void)
{
GPIO_InitTypeDef GPIO_InitStructure;
/* GPIOA Configuration:TIM3 Channel1, 2, 3 and 4 as alternate function push-pull */
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6 ;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; `
GPIO_Init(GPIOA, &GPIO_InitStructure);
}
/******************* (C) COPYRIGHT 2011 STMicroelectronics *****END OF FILE****/
[/mw_shl_code]
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发表于 2014-8-13 14:03:43
楼主
发表于 2014-8-14 23:04:32
