一 电路

注意：J5跳帽接到2~3引脚，使按键S4-S5四个按键的另外一端接地，从而成为4个独立按键。

二 独立按键工作原理

三 代码

代码1：按下S7点亮L1指示灯，松开按键，指示灯熄灭，按下S6点亮L2指示灯，按下S5点亮L3指示灯，按下S4点亮L4指示灯。

#include "reg52.h"

void Delay(unsignde int t)
{
  while(t--);
}//实现延时功能的函数
 
void InitHC138(unsigned char n)
{
 switch (n)
 { 
   case 4;
      HC138_C = 1;
      HC138_B = 0;
      HC138_A = 0;//输出Y4
   break;
   case 5;
      HC138_C = 1;
      HC138_B = 0;
      HC138_A = 1;//输出Y5
   break;
case 4;
      HC138_C = 1;
      HC138_B = 1;
      HC138_A = 0;//输出Y6
   break;
   case 5;
      HC138_C = 1;
      HC138_B = 1;
      HC138_A = 1;//输出Y7
   break;
 }
}//锁存器选择

void dulianjian()
{
  if(S7 == 0)
  {
   Delay(100);
    if(S7 == 0)
    {
      L1 = 0;
      while(S7 == 0)
      L1 = 1;
     }
    }

   if(S6 == 0)
   {
   Delay(100);
    if(S6 == 0)
    {
      L2 = 0;
      while(S5 == 0)
      L2 = 1;
     }
    }

   if(S5 == 0)
   {
   Delay(100);
    if(S5 == 0)
    {
      L3 = 0;
      while(S5 == 0)
      L3 = 1;
     }
    }

   if(S4 == 0)
   {
   Delay(100);
    if(S4 == 0)
    {
      L4 = 0;
      while(S4 == 0)
      L4 = 1;
     }
    }
}

void main()
{
  InitHC138(4);
  while(1)
  {
    dulianjian();
  }
}

代码2 ：  S7点亮L1时，S6不可执行操作，S5点亮L3，S4点亮L4；

S6点亮L2时，S7不可执行操作，S5点亮L5，S4点亮L6；

L1，L2均未被点亮时，S5，S4均不可执行操作。

#include "reg52.h"

void Delay(unsignde int t)
{
  while(t--);
}//实现延时功能的函数
 
void InitHC138(unsigned char n)
{
 switch (n)
 { 
   case 4;
      HC138_C = 1;
      HC138_B = 0;
      HC138_A = 0;//输出Y4
   break;
   case 5;
      HC138_C = 1;
      HC138_B = 0;
      HC138_A = 1;//输出Y5
   break;
case 4;
      HC138_C = 1;
      HC138_B = 1;
      HC138_A = 0;//输出Y6
   break;
   case 5;
      HC138_C = 1;
      HC138_B = 1;
      HC138_A = 1;//输出Y7
   break;
 }
}//锁存器选择

unsigned char stat_k = 0;
void dulianjian()
{
  if(S7 == 0)
  {
   Delay(100);
    if(stat_k == 0)
    {
      L1 = 0;
      stat_k = 1;
    }
      else if(stat_k = 1)
      L1 = 1;
      stat_k = 0;
     }
    }

   
  if(S6 == 0)
  {
   Delay(100);
    if(stat_k == 0)
    {
      L2 = 0;
      stat_k = 2;
    }
      else if(stat_k = 2)
      L2 = 1;
      stat_k = 0;
     }
    }

   if(S5 == 0)
  {
   Delay(100);
    if(stat_k == 1)
    {
      L3 = 0;
      while(S5 == 0);
      L3 = 1;
    }
      else if(stat_k = 2)
      L5 = 0;
      while(S5 == 0);
      L5 = 1;
     }
    }
   if(S4 == 0)
  {
   Delay(100);
    if(stat_k == 1)
    {
      L4 = 0;
      while(S5 == 0);
      L4 = 1;
    }
      else if(stat_k = 2)
      L6 = 0;
      while(S5 == 0);
      L6 = 1;
     }
    }
}

void main()
{
  InitHC138(4);
  while(1)
  {
    dulianjian();
  }
}