__interrupt void TimerISR(void)
{ static unsigned Cntr=0;
   Cntr+=1;
   __enable_interrupt();
   if (Cntr<2) key_scan_func(); // вызов функции сканирования клавиатуры, только если не было вложенного прерывания
   ...
   Cntr-=1;
}

#define     StartDelay 25
#define     NextDelay 3

const char * const key_name[LastKbdEvent+1]=
    {    "",name1,name2, name3, name4, name5, name6, name7 };


__no_init char kbd_status0;
__no_init char kbd_status1;
__no_init char kbd_status2;
__no_init char kbd_status3;
__no_init char kbd_status4;

__no_init char interrupt_counter;
__no_init char found_events;
__no_init char old_pressed_keys;
__no_init char pressed_counter;
__no_init char pressed_keys;
          char prescaler;

char DnPressed(void)
{   if (pressed_keys==kDn) return 1;
    else return 0;
}
char UpPressed(void)
{   if(pressed_keys==kUp) return 1;
    else return 0;
}
char NoPressed(void)
{   if (!pressed_keys) return 1;
    else return 0;
}


void InitKbd(void)
{
  kbd_status3=kbd_status2=kbd_status1=kbd_status0=0;
  found_events=0;
}


void KbdService(void)    // into timer interrupt 1 ms
{   if (prescaler<4)  { prescaler++; return;}
    prescaler=0;
            switch (interrupt_counter)     // to reduce time of function
    {
    case    0:    interrupt_counter=1;        //refresh statuses
            kbd_status3=kbd_status2;
            kbd_status2=kbd_status1;
            kbd_status1=kbd_status0;
            kbd_status0=Kbd;
            interrupt_counter=interrupt_counter;
            break;

    case    1:    interrupt_counter=2;        //check pressed key every tic
            pressed_keys=kbd_status0&kbd_status1&kbd_status2;
            if (pressed_keys&(~kbd_status3))
                if (bSound==SoundAlwaysOn) Beep(5,1);
            found_events|=pressed_keys&(~kbd_status3);        // found edge
            if ((pressed_keys==kUp+kDn)&&  // now this two keys
                ((~kbd_status3)&(kUp+kDn)))//and before it wasn't so
                {found_events|=kUpDn;    // set new bit
                found_events&=~(kUp+kDn);    break; } //reset usual bits
            if ((pressed_keys==kUp+kSt)&&  // now this two keys
                ((~kbd_status3)&(kUp+kSt)))//and before it wasn't so
                {found_events|=kUpSt;    // set new bit
                found_events&=~(kUp+kSt);    break; }//reset usual bits                
            if ((pressed_keys==kDn+kSt)&&  // now this two keys
                ((~kbd_status3)&(kDn+kSt)))//and before it wasn't so
                {found_events|=kDnSt;    // set new bit
                found_events&=~(kDn+kSt); break; }    //reset usual bits                    
        break;            
                
    case    2:    interrupt_counter=3;        //check if key the same as before
            if ((pressed_keys&kUp)||(pressed_keys&kDn))    //key for repeat
            {    if (pressed_keys==old_pressed_keys) // same key?
                {    if (pressed_counter)         // yes, time over?
                    {pressed_counter--;}      //No
                    else     {    pressed_counter=NextDelay;        //Yes
                            found_events=pressed_keys; }        //reset
                    }
                else                                            // other key
                    {pressed_counter=StartDelay;    
                    }
            };
            old_pressed_keys=pressed_keys;
            break;
    case    3:    interrupt_counter++;
                    break;
    default: interrupt_counter=0;
    }
}

unsigned char keyb;         // глобальная переменная, состояние клавиатуры
unsigned char kcnt;          // счетчик времени события "кнопка нажата"
...
//    Опрос клавиатуры, вызывается из подпрограммы
//    обработки прерывания по таймеру (каждые 4 мс)
//
void rd_keyb(void)  
{
    unsigned char st;
    st = ~PINC;                                              // читаем состояние кнопок
    if (st == 0) kcnt=0; else kcnt++;
    if (kcnt == 20) keyb=st;                            // таймаут антидребезга
    if (kcnt == 120) { keyb=st; kcnt -= 60; }   // автоповтор
}

; Time slot
; Pushbuttons #00-07 status
    in        PB00_07_In,PIND
    eor        PB00_07_In_Aux,PB00_07_In
    and        PB00_07_Stat,PB00_07_In_Aux
    com        PB00_07_In_Aux
    and        PB00_07_In_Aux,PB00_07_In
    or        PB00_07_Stat,PB00_07_In_Aux
    mov        PB00_07_In_Aux,PB00_07_In