程序代码：

#include "REG51.h"
#include "intrins.h"
#include <stdio.h>
#include <string.h>    

#define uchar  unsigned char
/*************************
    模拟SPI接口I/O定义
*************************/
sbit    spi_cs=P2^7; 
sbit    spi_di=P4^4; 
sbit    spi_clk=P4^1;
sbit    spi_do=P4^5;
void SomeNOP()
{
  _nop_();
  _nop_();
  _nop_();
  _nop_();
  _nop_();
  _nop_();
  _nop_();
  _nop_();

 }
/*******************************
    向SPI器件写入一个字节数据
*******************************/
void spi_write(unsigned char spi_dat) 
{ 
    unsigned  char  i; 
    spi_cs=0; 
    for  (i=0;i<8;i++) 
    {  
        spi_clk=0;
        if((spi_dat & 0x80)==0x80)
        {
            spi_di=1;  //写入最高位
        }
        else
            spi_di=0;
        SomeNOP(); 
        spi_clk=1;  
        spi_dat=(spi_dat<<1);  //左移一位，依次写入
    }
    spi_clk=0; 
    //spi_cs=1;
} 
/********************************
  从SPI器件读出一个字节数据
********************************/
unsigned char spi_read() 
{ 
    unsigned char i,spi_dat; 
    spi_cs=0;
    spi_clk=1; 
    for (i=0;i<8;i++)                     
    {                                
        spi_clk=0;                                   
        spi_dat=(spi_dat<<1);  //xxxxxxx0
        spi_clk=1;                                                                
        if(spi_do==1)
        {
            spi_dat|=0x01;  //xxxxxxx0|00000001        
        }
        else
        {
            spi_dat&=~0x01;  //xxxxxxx0&11111110                
        }
    spi_clk=0;                      //从高到低位依次移入
    //spi_cs=1;
    }
    return spi_dat; 
}



void spiwrite_start()
{
    EA = 0;
    spi_cs = 0;
    spi_clk = 0;
    spi_di = 1;
    SomeNOP();
    spi_clk = 1;
    SomeNOP();
    spi_clk = 0;
    spi_di = 0 ;
    SomeNOP();
    spi_clk = 1;
    //spi_cs = 1;
}
void spiread_start()
{
    EA = 0;
    spi_cs = 0;
    spi_clk = 0;
    spi_do = 1;
    SomeNOP();
    spi_clk = 1;
    SomeNOP();
    spi_clk = 0;
    spi_do = 1;
    SomeNOP();
    spi_clk = 1;
    //spi_cs = 1;
}


//写一个数据
void Write_OneByte(unsigned char addr,unsigned char ddata)
{
    spiwrite_start();
    SomeNOP();
    spi_write(addr);
    SomeNOP();
    spi_write(ddata);
    spi_cs = 1;
    SomeNOP();
}


//读一个数据
unsigned char Read_OneByte(unsigned char addr)
{
    uchar temp;
    spiread_start();
    SomeNOP();
    spi_write(addr);  //先写入地址，设置写
    SomeNOP();
    //spiread_start();
    //SomeNOP();
    temp = spi_read();
    spi_cs = 1;
    SomeNOP();
    return temp; 
}