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该设计不用二极管能接6键，3只二极管能接12键，6只二极管能接18键，9只二极管能接21键，第22键要单独占用3只二极管最不化算。
实验用89S51作试验，电路接线就是P1.2,P1.3,P1.4接键盘，P1.0接显示器。

源程序：

/*==================================================================*
*                   3个IO接识别22键测试程序                         *
*       ------------------------------------------------            *
*       MCU:     AT89C2051                                          *
*       OSC:     12M cysytel                                        *
*       程序设计:Cowboy                                             *
*       程序版本:V1.0                                               *
*==================================================================*/
#include <reg52.h>
//================== IO口线连接 ==================
sbit Bus          = P1^0;
sbit IO_a         = P1^4;
sbit IO_b         = P1^3;
sbit IO_c         = P1^2;
//================== 变量声明 ====================
unsigned char Disp_buf[3];
unsigned char Dig;
unsigned char Key_count;
unsigned char bdata Key_state;    
sbit KB0 = Key_state^0;
sbit KB1 = Key_state^1;
sbit KB2 = Key_state^2;
sbit KB3 = Key_state^3;
sbit KB4 = Key_state^4;
sbit KB5 = Key_state^5;
//================== 表格数据 ====================
code unsigned char LED_font[24]=
{
        0x84,0x9f,0xa2,0x8a,0x99,0xc8,0xc0,0x9e,0x80, //012345678
        0x88,0x90,0xc1,0xe4,0x83,0xe0,0xf0,0xff,0xfb, //9abcdef -
};
code unsigned char Key_tab[64]=     //键码映射表
{//  0  1  2  3  4  5  6  7  8  9   
        22, 0, 2, 0, 0, 0, 0, 0, 4, 0, //0
         0, 0, 0, 0, 0,18, 0, 0, 0, 0, //1X
         0, 0, 0, 0, 0, 0, 3,14, 0, 0, //2X
        20,10, 6, 0, 0, 0, 0, 0, 1,19, //3X
         0, 5, 0, 0, 0,15, 0,11, 0, 0, //4X
         0,17, 0, 0,13, 8, 0,21, 0, 9, //5X
        16,12, 7, 0                    //6X
};
//=============== 检测按键 =================
void Key_scan()
{   
    unsigned char i;
    Key_count --;                        //扫描次序
    Key_count &= 3;
    switch (Key_count)                //按次序处理
    {
        case 2:                           //第一轮扫描
        KB0 = IO_b; 
        KB1 = IO_c; 
        IO_a = 1;
        IO_b = 0;
        break;
        case 1:                        //每二轮扫描
        KB2 = IO_c;
        KB3 = IO_a;
        IO_b = 1;
        IO_c = 0;
        break;
        case 0:                        //每三轮扫描
        KB4 = IO_a;
        KB5 = IO_b;
        IO_c = 1;
        break;
        default:                        //每四轮扫描
        if (!IO_a) KB0 = 0;
        if (!IO_b) KB2 = 0;
        if (!IO_c) KB4 = 0;
        IO_a = 0;
        //======更新显示缓冲区=======
        i = Key_tab[Key_state];
        if (i == 0)
        {
            Disp_buf[2] = 0x11;            //显示三横
            Disp_buf[1] = 0x11;
            Disp_buf[0] = 0x11;
        }
        else
        {
            Disp_buf[2] = 0x0c;     //字符"C"
            Disp_buf[1] = i / 10;   //键码十位
            Disp_buf[0] = B;        //键码个位
        }
        Key_state = 0;
    }
}    
/*===================================================================
                    ONE WIRE 显示总线驱动程序       
===================================================================*/
//=============== 发送一位 =================
void Send_bit(bit Dat)    
{    
    unsigned char i = 3;
    if (!Dat) Bus = 0;
    else
    {
        Bus = 0;
        Bus = 1;
    }
    while(--i);                 //延时8us    
    Bus = 1;
}    
//=============== 总线驱动 =================
void Bus_drive()
{
    unsigned char i = 0;
    unsigned char Sdat;
    Send_bit(1);                        //Bit6消隐
    do Bus = 1; while(--i);             //延时768us
    do Bus = 0; while(--i);             //延时768us
    Bus = 1;
    Sdat = LED_font[Disp_buf[Dig++]];   //获取显示数据
    Send_bit(Sdat & 0x01);              //发送位0        
    Send_bit(Sdat & 0x02);              //发送位1        
    Send_bit(Sdat & 0x04);              //发送位2        
    Send_bit(Sdat & 0x08);              //发送位3        
    Send_bit(Sdat & 0x10);              //发送位4        
    Send_bit(Sdat & 0x20);              //发送位5        
    Send_bit(Dig  & 0x01);              //发送位选1        
    Send_bit(Dig  & 0x02);              //发送位选2
    while(--i);                         //延时512us
    Send_bit(Sdat & 0x40);              //发送位6
    for (i = 7;i > 0;i--) Send_bit(1);  //位6移至Dout
    if (Dig == 3) Dig = 0;
}     
/*===================================================================
                    延时 5ms 程序       
===================================================================*/
void Delay_5ms()        
{    
    while(!TF1);    
    TF1 = 0;    
    TH1 = (- 5000) / 256;
    TL1 = (- 5000) % 256;
}    
/*===================================================================
                        主程序       
===================================================================*/
void main()
{
    TMOD = 0x10;            //定时器1，16位模式
    TCON = 0xc0;            //TR1=1;TF1=1;
    while(1)                //主循环
    {
        Bus_drive();        //显示总线驱动 
        Key_scan();         //检测按键
        Delay_5ms();        //延时5MS    
    }
}