通常单片机的双机通信有以下4中方式通信：

TTL电平通信（双机串行口直接互连）、RS-232C通信、RS-422A通信、RS-485通信等。

TTL电平通信时，单片机A的TXD端接单片机B的RXD端，单片机B的RXD端接B的TXD端。但是两个单片机的地线必须要共地，即把他们的系统电源地线要接在一起。

主机按键

#include <reg52.h>
#define uchar unsigned char 
#define uint unsigned int
void delayms(uint xms)
{
uint i,j;
for(i=xms;i>0;i--)
for(j=110;j>0;j--);
}
void send(uchar key_num)
{
SBUF=key_num;
while(!TI);
TI=0;
}
void matrixkeyscan()
{
uchar temp,key;
P3=0xfe;
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
delayms(10);
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
temp=P3;
switch(temp)
{
case 0xee:
key=0;
break;
case 0xde:
key=1;
break;
case 0xbe:
key=2;
break;
case 0x7e:
key=3;
break;
}
while(temp!=0xf0)
{
temp=P3;
temp=temp&0xf0;
}
send(key);
}
}
P3=0xfd;
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
delayms(10);
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
temp=P3;
switch(temp)
{
case 0xed:
key=4;
break;
case 0xdd:
key=5;
break;
case 0xbd:
key=6;
break;
case 0x7d:
key=7;
break;
}
while(temp!=0xf0)
{
temp=P3;
temp=temp&0xf0;
}
send(key);
}
}
P3=0xfb;
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
delayms(10);
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
temp=P3;
switch(temp)
{
case 0xeb:
key=8;
break;
case 0xdb:
key=9;
break;
case 0xbb:
key=10;
break;
case 0x7b:
key=11;
break;
}
while(temp!=0xf0)
{
temp=P3;
temp=temp&0xf0;
}
send(key);
}
}
P3=0xf7;
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
delayms(10);
temp=P3;
temp=temp&0xf0;
if(temp!=0xf0)
{
temp=P3;
switch(temp)
{
case 0xe7:
key=12;
break;
case 0xd7:
key=13;
break;
case 0xb7:
key=14;
break;
case 0x77:
key=15;
break;
}
while(temp!=0xf0)
{
temp=P3;
temp=temp&0xf0;
}
send(key);
}
}
}


void main()
{
TMOD=0x02;
TH1=0xfd;
TL1=0xfd;
TR1=1;
SM0=0;
SM1=1;
EA=1;
ES=1;
while(1)
{
matrixkeyscan();//不停调用键盘扫描程序
}
}

从机 显示

#include<reg52.h>
#define uchar unsigned char 
#define uint unsigned int 
sbit dula=P2^6;
sbit wela=P2^7;
uchar code table[]={
0x3f,0x06,0x5b,0x4f,
0x66,0x6d,0x7d,0x07,
0x7f,0x6f,0x77,0x7c,
0x39,0x5e,0x79,0x71
};
void display(uchar num)
{
P0=table[num];
dula=1;
dula=0;
}


void main()
{
TMOD=0x20;
TH1=0xfd;
TL1=0xfd;
TR1=1;
REN=1;
SM0=0;
SM1=1;
EA=1;
ES=1;
P0=0xc0;
wela=1;
wela=0;
while(1);
}


void ser() interrupt 4
{
uchar a;
RI=0;
a=SBUF;
display(a);
}

单片的双机通信