普通情况下一个按键可用普通IO口或者ADC端口做按键扫描。两种原理图如下：

AD按键扫描与长短按键可以用如下的C代码实现：

typedef unsigned char u8;
typedef unsigned int u16;
void AdcInit(void);
u16 AdcConverts(unsigned char Channel);
u8 KeyRead(void)//读取键的状态
{
    u16 keyAdcValue = 0;
    keyAdcValue = AdcConverts(KEY_CHANNEL);
    if ((keyAdcValue < (KEY0_ADC + KEY_ADC_DELTA)) && (keyAdcValue >(KEY0_ADC - KEY_ADC_DELTA))){
        return KEY_0;
    }
    else if ((keyAdcValue < (KEY1_ADC + KEY_ADC_DELTA)) && (keyAdcValue >(KEY1_ADC - KEY_ADC_DELTA))){
        return KEY_1;
    }
    else if........
    }
    else{
        return KEY_NULL;
    }
}
void KeyScan(void)
{
    static unsigned char g_ucLastKeypad, KeyNum, ShortKey, LongKey;
    static unsigned char KeyValue = KEY_NULL;
    unsigned char KeyStatus = 0;
    KeyStatus = KeyRead();
    ShortKey = ShortKey;
    LongKey = LongKey;
    if(g_ucLastKeypad == KEY_NULL && KeyStatus != g_ucLastKeypad){                //按键刚被按下
        KeyNum = 0;
        ShortKey = 0;
        LongKey = 0;
        KeyValue = KEY_NULL;
    }
    else if(KeyStatus == g_ucLastKeypad && KeyStatus != KEY_NULL){                //按键正被按着
        KeyNum++;
        if(KeyNum == KEY_LONG_TIMES){
            ShortKey = 0;
            LongKey = 1;
            KeyValue = g_ucLastKeypad;
        }
    }
    else if(KeyStatus == KEY_NULL && KeyStatus != g_ucLastKeypad){                //按键被放开
        if(KeyNum < KEY_LONG_TIMES && KeyNum > KEY_SHORT_TIMES){
            KeyNum = 0;
            ShortKey = 1;
            LongKey = 0;
            KeyValue=  g_ucLastKeypad;
        }
    }
    else{
        KeyNum = 0;
        ShortKey = 0;
        LongKey = 0;
        KeyValue = KEY_NULL;
    }
    g_ucLastKeypad = KeyStatus;
     
  }

普通IO口的按键的长短按也可以利用AD的识别来做，唯一不同就是按键扫描方式不一样。下面给出一个按键识别实例。

u8 KeyScan(void)//0为无按键按下，1为短按，2为长按。
{
    static u8 Press_Flag=0,g_Press_Flag=0,ReturnFlag=0;
    static u16 KeyNum=0;
    u8 KeyStatus=0;
    KeyStatus=ReadGPIOKey();
    if(Press_Flag==0)
    {
        if(KeyNum<1)
        {
            KeyNum++;
            if(KeyStatus==0) KeyNum=0;
            return 0;
        }
        else
        {
            KeyNum=0;
            Press_Flag=1;
            return 0;
        }
    }
    else
    {
        if(KeyNum <= 15)
        {
            if(KeyStatus==1)
            {    
                KeyNum++;
                return 0;
            }
            
            if(g_Press_Flag<1)                                                                                                                      
            {    
                if(KeyStatus==0) g_Press_Flag++;
            }
            else
            {
                Press_Flag=0;
                g_Press_Flag=0;
                KeyNum=0;
                return 1;
            }
        }
        else if(KeyNum < 400 && KeyNum >15)
        {
            if(KeyStatus==1)
            {    
                KeyNum++;
                return 0;
            }
            
            if(g_Press_Flag<1)                                                                                                                      
            {    
                if(KeyStatus==0) g_Press_Flag++;
            }
            else
            {
                Press_Flag=0;
                g_Press_Flag=0;
                KeyNum=0;
                return 2;
            }
        }
        else if(KeyNum >= 400)
        {
            if(KeyStatus==1)
            {    
                if(ReturnFlag==0)
                {
                    KeyNum++;
                    ReturnFlag=1;
                    return 3;
                }
            }
            
            if(g_Press_Flag<1)
            {    
                if(KeyStatus==0) g_Press_Flag++;
            }
            else
            {                                                                                                
                Press_Flag=0;
                g_Press_Flag=0;
                ReturnFlag=0;
                KeyNum=0;
                return 0;
            }
        }
        return 0;
    }
    
}