为什么中间变量用了出现错误？

Question

为什么写iic 的时候读取用中间变量读不出来，比如unsigned char i,用 i = at24c02_writebyte(0x00,1)就不能显示出正确的数值

void main()
{
    unsigned char i = 0;
    P2 = 0xa0;
    P0 = 0x00;
    P2 = 0x00;    
    
    P2 = 0x80;
    P0 = 0xff;
    P2 = 0x00;   
    
    i = at24c02_writebyte(0x00,1);
    Delay(200);       
    while(1)
    {
        DisplaySMG_Bit(0x01,SMGNoDot_CA[i]);
        Delay(10);
    }
}

但是如果不用i这个中间变量就可以

```c
void main()
{
    P2 = 0xa0;
wanzheng    P0 = 0x00;
    P2 = 0x00;    
    
    P2 = 0x80;
    P0 = 0xff;
    P2 = 0x00;   
    
    at24c02_writebyte(0x00,1);
    Delay(200);     
    while(1)
    {
        DisplaySMG_Bit(0x01,SMGNoDot_CA[AT24C02_Readbyte(0x00)]);
        Delay(10);
    }
}

但是如果不用i这个中间变量就可以

```c

#include "reg52.h"
#include "iic.h"     
#define  AT24C02_ADD 0xa0
unsigned char SMGNoDot_CA[10] = {0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90}; 

void Delay(unsigned int t)
{
    while(t--);
}

//================
void DisplaySMG_Bit(unsigned char pos ,unsigned char value)
{
    P2 = 0xc0;
    P0 = pos;
    P2 = 0xe0;
    P0 = value;
}

//================

void at24c02_writebyte(unsigned char dizhi,unsigned char shuzhi)
{
    IIC_Start();
    IIC_SendByte(AT24C02_ADD);
    IIC_WaitAck();             
    IIC_SendByte(dizhi);     
    IIC_WaitAck();             
    IIC_SendByte(shuzhi);     
    IIC_WaitAck();   
    IIC_Stop();
}

unsigned char AT24C02_Readbyte(unsigned char dizhi)  
{
  unsigned char Data;    
    IIC_Start();
    IIC_SendByte(AT24C02_ADD); 
    IIC_WaitAck();            
    IIC_SendByte(dizhi);       
    IIC_WaitAck();  
  IIC_Start();    
    IIC_SendByte(AT24C02_ADD | 0x01); 
    IIC_WaitAck();    
    Data = IIC_RecByte(); 
    IIC_SendAck(1);
    IIC_Stop();
    return Data;
}

void main()
{
    P2 = 0xa0;
    P0 = 0x00;
    P2 = 0x00;    
    
    P2 = 0x80;
    P0 = 0xff;
    P2 = 0x00;   
    
    at24c02_writebyte(0x00,1);
    Delay(200);     
    while(1)
    {
        DisplaySMG_Bit(0x01,SMGNoDot_CA[AT24C02_Readbyte(0x00)]);
        Delay(10);
    }
}

Answer 1

函数 at24c02_writebyte 返回值类型为void，用i=at24c02_writebyte()是错误用法，这个函数不会给你返回任何东西；
而AT24C02_Readbyte有返回值就可以