写一个c51单片机测量脉冲频率的c语言程序，通过测量周期时间内的脉冲数量得到脉冲频率

以下是C语言程序的代码，用于测量脉冲频率：

#include <reg51.h>
#include <stdio.h>

#define CLK 22118400UL
#define BAUD 115200
#define TIMER_PRESCALER 12

sbit TEST_PIN = P1^0;

unsigned char receiveBuffer[16];
unsigned char receiveCounter = 0;

float frequency;

void initSerial()
{
    SCON = 0x50;
    TMOD &= 0x0F;
    TMOD |= 0x20;
    TH1 = 256 - CLK/(32*TIMER_PRESCALER*BAUD);
    TR1 = 1;
}

void receiveInterrupt() interrupt 4
{
    RI = 0;
    receiveBuffer[receiveCounter] = SBUF;
    receiveCounter++;

    if (receiveBuffer[receiveCounter-1] == '\n') {
        receiveBuffer[receiveCounter-1] = '\0';
        receiveCounter = 0;
        sscanf(receiveBuffer, "%f\r", &frequency);
    }
}

void main()
{
    unsigned long pulseCount = 0;
    unsigned long pulsePeriod = 0;
    unsigned long start = 0;

    initSerial();
    TMOD &= 0xF0;
    TMOD |= 0x01;
    TEST_PIN = 0;

    while(1) {
        TEST_PIN = 1;

        while(!TEST_PIN);
        TR0 = 1;
        while(TEST_PIN);
        TR0 = 0;

        pulseCount++;
        pulsePeriod += TH0 * 256 + TL0;

        if (pulseCount == 100) {
            frequency = 1.0/pulsePeriod*100*TIMER_PRESCALER*CLK;
            printf("%.2f Hz\n", frequency);
            pulseCount = 0;
            pulsePeriod = 0;
        }

        start = TH0 * 256 + TL0;
        while ((TH0 * 256 + TL0) - start < (CLK/(TIMER_PRESCALER*100)))
            ;

    }
}

这个程序实现了通过测量一定时间内的脉冲数量来计算脉冲频率。程序中使用了定时器和外部触发脉冲来实现精确测量。具体来说，程序中使用了定时器 T0 来计算脉冲周期的时间，每测量到 100 个脉冲，就通过计算平均周期时间来计算脉冲频率。在本例中，使用的是 22118400Hz 的晶振。