STM32单片机电源端并联电容的重要性

如图&＃xff0c;笔者用TQFP(32-100PIN)0.55MM转直插的转接板焊了一个STM32F207VET6的板子。板上引出了SWD调试接口&＃xff08;仅占用PA13和PA14&＃xff09;&＃xff0c;USART1串口引脚&＃xff0c;插了一个触摸传感器和蜂鸣器模块。

所要实现的功能是&＃xff1a;用手触碰一下触摸传感器后&＃xff0c;蜂鸣器响一声。

接触摸传感器模块输出信号接到PA0口上。在没有接电源电容之前&＃xff0c;每一次单片机复位&＃xff08;无论是软件复位还是按下复位键复位&＃xff09;&＃xff0c;PA0上会自动产生一个异常的高电平&＃xff0c;要等上将近10秒才会回到低电平&＃xff0c;然后触摸传感器才能正常工作。每次复位的时候蜂鸣器都会响一下&＃xff0c;10秒之内按触摸键都没有反应。

后来我接了一个4.7μF的电解电容器和两个100nF的无极性电容器&＃xff0c;问题就解决了。单片机复位后蜂鸣器不会响&＃xff0c;手按触摸键后马上就能响&＃xff0c;不用再等10秒。

还有&＃xff0c;不接电容器&＃xff0c;串口下载以及SWD/JTAG下载有时也会受影响。特别是没有外接25MHz的HSE晶振的情况下&＃xff0c;Flash Loader Demo&＃xff08;串口烧写STM32的工具&＃xff09;经常连不上芯片。

这说明&＃xff0c;这些电容对保证单片机以及外围器件运行的可靠性非常重要。

【20-Pin的SWD调试接口连线】

【测试用的程序】

#include
#include int fputc(int ch, FILE *fp)
{if (fp &＃61;&＃61; stdout){if (ch &＃61;&＃61; &＃39;\n&＃39;){while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) &＃61;&＃61; RESET);USART_SendData(USART1, &＃39;\r&＃39;);}while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) &＃61;&＃61; RESET);USART_SendData(USART1, ch);}return ch;
}void showclk(void)
{RCC_ClocksTypeDef clocks;RCC_GetClocksFreq(&clocks);printf("USART1->BRR&＃61;%d\n", USART1->BRR);printf("SYSCLK&＃61;%dHz HCLK&＃61;%dHz PCLK1&＃61;%dHz PCLK2&＃61;%dHz\n", clocks.SYSCLK_Frequency, clocks.HCLK_Frequency, clocks.PCLK1_Frequency, clocks.PCLK2_Frequency);printf("HSERDY&＃61;%d, SYSCLK&＃61;%d\n", RCC_GetFlagStatus(RCC_FLAG_HSERDY), RCC_GetSYSCLKSource());
}int main(void)
{EXTI_InitTypeDef exti;GPIO_InitTypeDef gpio;TIM_OCInitTypeDef oc;TIM_TimeBaseInitTypeDef tim;USART_InitTypeDef usart;RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);RCC_APB1PeriphClockCmd(RCC_APB1Periph_PWR | RCC_APB1Periph_TIM2, ENABLE);RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);PWR_BackupAccessCmd(ENABLE);GPIO_PinAFConfig(GPIOA, GPIO_PinSource3, GPIO_AF_TIM2);gpio.GPIO_Mode &＃61; GPIO_Mode_AF;gpio.GPIO_OType &＃61; GPIO_OType_PP;gpio.GPIO_Pin &＃61; GPIO_Pin_3;gpio.GPIO_PuPd &＃61; GPIO_PuPd_NOPULL;gpio.GPIO_Speed &＃61; GPIO_Speed_2MHz;GPIO_Init(GPIOA, &gpio);GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1);gpio.GPIO_Pin &＃61; GPIO_Pin_9;gpio.GPIO_Speed &＃61; GPIO_Speed_50MHz;GPIO_Init(GPIOA, &gpio);USART_StructInit(&usart);usart.USART_BaudRate &＃61; 115200;USART_Init(USART1, &usart);USART_Cmd(USART1, ENABLE);showclk();if (RCC_GetFlagStatus(RCC_FLAG_LSERDY) &＃61;&＃61; SET)printf("LSE on!\n");else{RCC_ITConfig(RCC_IT_LSERDY, ENABLE);NVIC_EnableIRQ(RCC_IRQn);RCC_LSEConfig(RCC_LSE_ON);}TIM_UpdateRequestConfig(TIM2, TIM_UpdateSource_Regular);TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);NVIC_EnableIRQ(TIM2_IRQn);TIM_TimeBaseStructInit(&tim);tim.TIM_Period &＃61; 9;tim.TIM_Prescaler &＃61; 1699;TIM_TimeBaseInit(TIM2, &tim);oc.TIM_OCMode &＃61; TIM_OCMode_PWM2;oc.TIM_OCPolarity &＃61; TIM_OCPolarity_High;oc.TIM_OutputState &＃61; TIM_OutputState_Enable;oc.TIM_Pulse &＃61; 4;TIM_OC4Init(TIM2, &oc);exti.EXTI_Line &＃61; EXTI_Line0;exti.EXTI_LineCmd &＃61; ENABLE;exti.EXTI_Mode &＃61; EXTI_Mode_Interrupt;exti.EXTI_Trigger &＃61; EXTI_Trigger_Rising_Falling;EXTI_Init(&exti);NVIC_EnableIRQ(EXTI0_IRQn);while (1)__WFI();
}void EXTI0_IRQHandler(void)
{EXTI_ClearITPendingBit(EXTI_Line0);if (GPIO_ReadInputDataBit(GPIOA, GPIO_Pin_0) &＃61;&＃61; Bit_SET){TIM_Cmd(TIM2, ENABLE);printf("Touch!\n");}elseprintf("Released!\n");
}void RCC_IRQHandler(void)
{if (RCC_GetITStatus(RCC_IT_LSERDY) &＃61;&＃61; SET){RCC_ClearITPendingBit(RCC_IT_LSERDY);printf("LSE ready!\n");}
}void TIM2_IRQHandler(void)
{static uint16_t counter &＃61; 0;if (TIM_GetITStatus(TIM2, TIM_IT_Update) &＃61;&＃61; SET){TIM_ClearITPendingBit(TIM2, TIM_IT_Update);counter&＃43;&＃43;;if (counter &＃61;&＃61; 999)TIM_SelectOnePulseMode(TIM2, TIM_OPMode_Single);else if (counter &＃61;&＃61; 1000){counter &＃61; 0;TIM_SelectOnePulseMode(TIM2, TIM_OPMode_Repetitive);}}
}