用51单片机设计一个数字时钟

设计一个数字时钟可以分为以下几个步骤：

1. 硬件设计

- 选用合适的51单片机，如STC89C52等。
- 选用合适的时钟芯片，如DS1302等。
- 选用合适的数码管显示模块，如共阳数码管等。

2. 软件设计

- 使用C语言编写程序，在主函数中初始化单片机和时钟芯片。
- 在程序中设置一个定时器中断，用于控制时钟的运行。
- 在定时器中断服务函数中，更新时钟的时间，并将时间显示在数码管上。

具体的实现过程可以参考以下代码：

#include <reg51.h>

#define uchar unsigned char
#define uint unsigned int

sbit DS1302_SCLK = P2^0;
sbit DS1302_IO = P2^1;
sbit DS1302_RST = P2^2;
sbit DIG1 = P1^0;
sbit DIG2 = P1^1;
sbit DIG3 = P1^2;
sbit DIG4 = P1^3;
sbit DIO = P3^4;
sbit RCLK = P3^5;
sbit SRCLK = P3^6;
sbit OE = P3^7;

uchar code digCode[] = {
    0xc0, 0xf9, 0xa4, 0xb0, 0x99, 0x92, 0x82, 0xf8, 0x80, 0x90
};

uchar year, month, date, week, hour, minute, second;

void delay(uchar t) {
    uchar i, j;
    for (i = t; i > 0; i--) {
        for (j = 110; j > 0; j--);
    }
}

uchar ds1302ReadByte() {
    uchar i, dat = 0;
    for (i = 0; i < 8; i++) {
        DS1302_SCLK = 0;
        dat >>= 1;
        if (DS1302_IO) {
            dat |= 0x80;
        }
        DS1302_SCLK = 1;
    }
    return dat;
}

void ds1302WriteByte(uchar dat) {
    uchar i;
    for (i = 0; i < 8; i++) {
        DS1302_SCLK = 0;
        DS1302_IO = dat & 0x01;
        dat >>= 1;
        DS1302_SCLK = 1;
    }
}

void ds1302Write(uchar addr, uchar dat) {
    DS1302_RST = 0;
    DS1302_SCLK = 0;
    DS1302_RST = 1;
    ds1302WriteByte(addr);
    ds1302WriteByte(dat);
    DS1302_RST = 0;
    DS1302_SCLK = 0;
}

uchar ds1302Read(uchar addr) {
    uchar dat;
    DS1302_RST = 0;
    DS1302_SCLK = 0;
    DS1302_RST = 1;
    ds1302WriteByte(addr | 0x01);
    dat = ds1302ReadByte();
    DS1302_RST = 0;
    DS1302_SCLK = 0;
    return dat;
}

void ds1302Init() {
    uchar i;
    ds1302Write(0x8E, 0x00);
    for (i = 0; i < 7; i++) {
        ds1302Write(i, 0x00);
    }
    ds1302Write(0x8E, 0x80);
}

void ds1302ReadTime() {
    uchar i;
    year = ds1302Read(0x8D);
    month = ds1302Read(0x89);
    date = ds1302Read(0x87);
    week = ds1302Read(0x8B);
    hour = ds1302Read(0x85);
    minute = ds1302Read(0x83);
    second = ds1302Read(0x81);
}

void ds1302WriteTime() {
    ds1302Write(0x8E, 0x00);
    ds1302Write(0x8D, year);
    ds1302Write(0x89, month);
    ds1302Write(0x87, date);
    ds1302Write(0x8B, week);
    ds1302Write(0x85, hour);
    ds1302Write(0x83, minute);
    ds1302Write(0x81, second);
    ds1302Write(0x8E, 0x80);
}

void display(uchar dig, uchar num) {
    DIO = 1;
    RCLK = 0;
    SRCLK = 0;
    if (dig == 1) {
        DIG1 = 1;
        DIG2 = 0;
        DIG3 = 0;
        DIG4 = 0;
    } else if (dig == 2) {
        DIG1 = 0;
        DIG2 = 1;
        DIG3 = 0;
        DIG4 = 0;
    } else if (dig == 3) {
        DIG1 = 0;
        DIG2 = 0;
        DIG3 = 1;
        DIG4 = 0;
    } else if (dig == 4) {
        DIG1 = 0;
        DIG2 = 0;
        DIG3 = 0;
        DIG4 = 1;
    }
    OE = 1;
    shiftOut(digCode[num]);
    OE = 0;
}

void shiftOut(uchar dat) {
    uchar i;
    for (i = 0; i < 8; i++) {
        DIO = dat & 0x80;
        dat <<= 1;
        SRCLK = 0;
        SRCLK = 1;
    }
    RCLK = 0;
    RCLK = 1;
}

void timer0Init() {
    TMOD &= 0xF0;
    TMOD |= 0x01;
    TH0 = 0xFC;
    TL0 = 0x67;
    ET0 = 1;
    EA = 1;
    TR0 = 1;
}

void timer0() interrupt 1 {
    TH0 = 0xFC;
    TL0 = 0x67;
    ds1302ReadTime();
    second++;
    if (second == 60) {
        second = 0;
        minute++;
        if (minute == 60) {
            minute = 0;
            hour++;
            if (hour == 24) {
                hour = 0;
            }
        }
    }
    display(1, hour / 10);
    display(2, hour % 10);
    display(3, minute / 10);
    display(4, minute % 10);
}

void main() {
    ds1302Init();
    display(1, 0);
    display(2, 0);
    display(3, 0);
    display(4, 0);
    timer0Init();
    while (1);
}

该程序使用了DS1302时钟芯片和四个共阳数码管模块，实现了一个简单的数字时钟。程序中使用了定时器中断来控制时钟的运行，每一秒更新一次数码管的显示。