Extended application of single chip microcomputer-06 independent key

subject ：

Blue Bridge Cup MCU simulation schematic diagram ： Blue Bridge Cup MCU simulation schematic diagram .pdsprj- Handout document resources -CSDN library

Circuit diagram ： 

  Code ：

# include<reg52.h>

// Decoder 
sbit HC138_C = P2^7;
sbit HC138_B = P2^6;
sbit HC138_A = P2^5;
// LED
sbit L1 = P0^0;
sbit L2 = P0^1;
sbit L3 = P0^2;
sbit L4 = P0^3;
sbit L5 = P0^4;
sbit L6 = P0^5;
//  Independent keyboard 
sbit S7 = P3^0;
sbit S6 = P3^1;
sbit S5 = P3^2;
sbit S4 = P3^3;

void SwitchHC138(unsigned char channel)
{
	switch(channel)
	{
		case 4:
			HC138_C = 1;
			HC138_B = 0;
			HC138_A = 0;
		break;
		case 5:
			HC138_C = 1;
			HC138_B = 0;
			HC138_A = 1;
		break;
		case 6:
			HC138_C = 1;
			HC138_B = 1;
			HC138_A = 0;
		break;
		case 7:
			HC138_C = 1;
			HC138_B = 1;
			HC138_A = 1;
		break;
	}
}
void DelayKeys(unsigned char t)
{
	while(t--);
	
}
unsigned char flag=0;
void ScanKeys()
{
	if(S7 == 0)
	{
		DelayKeys(100);
		if(S7==0)
		{
			if(flag==0)
			{
				L1 = 0;
				flag=1;
			}
			else if(flag == 1)
			{
				L1 = 1;
				flag = 0;
			}while(S7 == 0);
		}
	}
	if(S6 == 0)
	{
		DelayKeys(100);
		if(S6==0)
		{
			if(flag==0)
			{
				L2 = 0;
				flag=2;
			}
			else if(flag == 2)
			{
				L2 = 1;
				flag = 0;
			}while(S6 == 0);
		}
	}
	if(S5 == 0)
	{
		DelayKeys(100);
		if(S5 == 0)
		{
			if(flag == 1)
			{
				L3 = 0;
				while(S5 == 0); // Close when you let go L3
				L3 = 1;
			}
			else if(flag == 2)// Close when you let go L4
			{
				L5 = 0;
				while(S5 == 0);
				L5 = 1;
			}
		}
	}
	if(S4 == 0)
	{
		DelayKeys(100);
		if(S4 == 0)
		{
			if(flag == 1)
			{
				L4 = 0;
				while(S4 == 0); // Close when you let go L3
				L4 = 1;
			}
			else if(flag == 2)// Close when you let go L4
			{
				L6 = 0;
				while(S4 == 0);
				L6 = 1;
			}
		}
	}
}

void Init()
{
	SwitchHC138(7);
	P0=0x00;
	SwitchHC138(5);
	P0=0x00;
	SwitchHC138(4);
	P0=0xff;
	
}
void main()
{
	Init();
	while(1)
	{
		ScanKeys();
	}
}