这是一篇 2017–2018 年的嵌入式学习笔记，保留当时的工具、代码和实验过程。 查看系列目录。

delay.h

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#include <main.h>

#ifndef  _DELAY_H
#define _DELAY_H

void delay_ms(uint timer);

#endif

delay.c

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#include "main.h"

void delay_ms(uint timer)
{
    uchar j = 124;
    while(timer--)
    {
        while(j--);
    }
}

iic.h

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#ifndef _IIC_H
#define _IIC_H 

#include <reg51.h>
#include "main.h"

sbit SDA = P2^7;
sbit SCL = P2^6;

#define IIC_DEVICE 0x40

void init_IIC();
void IIC_start();
void IIc_stop();
void ack();
void noack();
void IIC_write_byte(uchar dat);
uchar IIC_read_byte();
void write_IIC(uchar addr, uchar dat);
uchar read_IIC(uchar addr);
void delay();

#endif

iic.c

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#include <intrins.h>
#include <reg51.h>
#include "main.h"
#include "iic.h"

void delay()
{
    uchar i;
    for(i = 0; i < 8; i++)
    {
        _nop_();
    }
}

void init_IIC()
{
    SDA = 1;
    delay();
    SCL = 1;
    delay();
}

void IIC_start()
{
    SDA = 1;
    delay();
    SCL = 1;
    delay();
    SDA = 0;
    delay();
}

void IIc_stop()
{
    SDA = 0;
    delay();
    SCL = 1;
    delay();
    SDA = 1;
    delay();
}

void ack()
{
    uchar i = 0;
    SCL = 1;
    delay();

    while((SDA = 1)&&(i < 255))
    {
        i++;
    }

    SCL = 0;
    delay();
}

void noack()
{
    SDA = 1;
    delay();
    SCL = 1;
    delay();
    SCL  = 0;
    delay();
}

void IIC_write_byte(uchar dat)
{
    uchar i, tmp;
    tmp = dat;
    for (i = 0; i < 8; ++i)
    {
        tmp = tmp<<1;
        SCL = 0;
        delay();
        SDA = CY;
        delay();
        SCL = 1;
        delay();
    }
    SCL = 0;
    delay();
    SDA = 1;
    delay();
}

uchar IIC_read_byte()
{
    uchar i, k;
    SCL = 0;
    delay();
    SDA = 1;
    for (i = 0; i < 8; ++i)
    {
        SCL = 1;
        delay();
        k = (k<<1)|SDA;
        SCL  = 0;
        delay();
    }
    delay();
    return k;
}

void write_IIC(uchar addr, uchar dat)
{
    IIC_start();
    IIC_write_byte(IIC_DEVICE);
    ack();
    IIC_write_byte(addr);
    ack();
    IIC_write_byte(dat);
    ack();
    IIc_stop();
}

uchar read_IIC(uchar addr)
{
    uchar tmp;
    IIC_start();
    IIC_write_byte(IIC_DEVICE);
    ack();
    IIC_write_byte(addr);
    ack();

    IIC_start();
    IIC_write_byte(IIC_DEVICE|0x01);
    ack();
    IIC_read_byte();
    noack();
    IIc_stop();
    return tmp;
}

main.h

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#ifndef  _MAIN_H
#define _MAIN_H

#define uint unsigned int
#define uchar unsigned char

#endif

main.c

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#include <reg51.h>
#include "main.h"
#include "delay.h"
#include "iic.h"

#define DAT_ADDR 0X03

sbit LED1 = P2^0;
sbit LED2 = P2^1;

uchar g_ucDat;

void display(uchar dat)
{
    LED1 = 0;
    LED2 = 1;
    P0 = (dat%10);
    delay_ms(5);
    LED2 = 0;
    LED1 = 1;
    P0 = (dat/10);
    delay_ms(5);
}

void int0_init()
{
    EX0 = 1;
    IT0 = 1;
    EA = 1;
}

void int0_inter() interrupt 0
{
    g_ucDat++;
}

void main()
{
    uchar tmp = 0;
    
    g_ucDat = 0;
    int0_init();
    init_IIC();

    tmp = read_IIC(DAT_ADDR);
    if (tmp == 0xff)
    {
        tmp = 0;
        write_IIC(DAT_ADDR, tmp);
        delay_ms(10);
    }
    g_ucDat = tmp;

    while(1)
    {
        if(tmp != g_ucDat)
        {
            if(g_ucDat > 99)
            {
                g_ucDat = 1;
            }
            tmp = g_ucDat;
            write_IIC(DAT_ADDR, tmp);
        }
        display(tmp);
    }
}