将一个电阻和一个电容串联起来接地。最左边为电阻,电阻的最左端接单片机的PC1口,并设为输出。电阻和电容中间引出一根线,接到PC0口,设为输入。 最初PC1输出低电平,电容上没有电荷,PC0为低电平。 此时立即将PC1设为高电平,电容开始充电,PC0仍为低电平,过了一段时间后才变为高电平。也就是说PC0比PC1变化慢。将PC1设置回低电平后,也要过一段时间PC0才能变回低电平。 【计时用的程序】 #include <stm32f10x.h>
#define MODE 0 // MODE: 0->六位小数, 1->4位小数
#if MODE #define TPSC 7199 // 精度: 100us #define N 4 #else #define TPSC 71 // 精度: 1us #define N 6 #endif
uint8_t seg8[] = {0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90}; uint16_t num = 0;
void delay(void) { uint16_t i; for (i = 0; i < 20000; i++); }
void ser_in(uint8_t data) { uint8_t i; for (i = 0; i < 8; i++) { GPIOB->BRR = GPIO_BRR_BR9; // SCLK=PB9 if (data & 0x80) GPIOB->BSRR = GPIO_BSRR_BS7; // DIO=PB7 else GPIOB->BRR = GPIO_BRR_BR7; data <<= 1; GPIOB->BSRR = GPIO_BSRR_BS9; } }
void par_out(void) { GPIOB->BRR = GPIO_BRR_BR8; // RCLK=PB8 GPIOB->BSRR = GPIO_BSRR_BS8; }
void seg_scan(void) { uint8_t i; uint16_t numbuf = num; for (i = 0; i <= N; i++) { if (i == N) ser_in(seg8[numbuf % 10] & 0x7f); else ser_in(seg8[numbuf % 10]); ser_in(1 << i); par_out(); delay(); numbuf /= 10; } }
int main(void) { RCC->APB1ENR = RCC_APB1ENR_TIM6EN; RCC->APB2ENR = RCC_APB2ENR_IOPBEN | RCC_APB2ENR_IOPCEN; GPIOB->CRH = 0x00300033; GPIOB->CRL = 0x30000033; GPIOC->CRL = 0x34; TIM6->ARR = TIM_ARR_ARR; TIM6->PSC = TPSC; TIM6->CR1 = TIM_CR1_URS | TIM_CR1_OPM; TIM6->EGR = TIM_EGR_UG; TIM6->CR1 |= TIM_CR1_CEN; // 开始计时 GPIOC->BSRR = GPIO_BSRR_BS1; // 充电 while ((GPIOC->IDR & GPIO_IDR_IDR0) == 0); // 等待输出端的电平变为1 num = TIM6->CNT; // 记录时间 GPIOC->BRR = GPIO_BRR_BR1; // 放电 while (1) seg_scan(); }
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