Микроконтроллеры

__tiny volatile char    IntFlags;        // Various interrupt flags

#define    ENTER_BTN    (1<<3)        //  -- "Enter" button
#define    SETUP_BTN    (1<<4)        //  -- "Setup" button
#define    PROG_BTN     (1<<5)        //  -- "Program" button
#define    BUTN_MSK    (ENTER_BTN | SETUP_BTN | PROG_BTN)

Разбирайтесь

//
//    Constant definitions
//
#define    BTN_PRESSED    (1<<0)    // Any button is pressed
#define    BTN_AUTO    (1<<1)    // Auto repeat mode

//
//    Static variables
//
static char    BtnFlags;    // Various flags
static char    BtnDebounce;    // Debounce counter

//
// ** InitButtons    -- the routine initiates button port
//
void InitButtons(void)
    {
    INPUT_DDR    &= ~BUTN_MSK;
    INPUT_PULLUP    |= BUTN_MSK;
    BtnFlags = BtnDebounce = 0;
    }
//
// ** ReadBtns    -- the function returns the buttons state
//
char ReadBtns(void)
    {
    return ~INPUT_PORT & BUTN_MSK;
    }
//
// ** GetButtons    -- the function does button state check,
//            and returns 0 if the buttons are not pressed.
//
char GetButtons(void)
    {
    char    _temp;

    while (!(IntFlags & BUTTON_BIT));
    IntFlags &= ~BUTTON_BIT;
    if (IntFlags & TMO_BIT)            // Time-out return
        return 0;            //
    if (!(_temp = ReadBtns()))        // No button is pressed
        {
        return BtnFlags = BtnDebounce = 0;
        }
    TimoutCnt = 0;                // Clear time-out counter
    if (!(BtnFlags & BTN_PRESSED))
        {
        BtnFlags |= BTN_PRESSED;
        }
    else    {
        if (!(_temp & PROG_BTN))
            return 0;
        if (!(BtnFlags & BTN_AUTO))    //
            {
            if (++BtnDebounce < 80)
                return 0;
            BtnFlags |= BTN_AUTO;    // Set auto-repeat flag
            }
        else    {
            if (++BtnDebounce < 20)
                return 0;
            }
        BtnDebounce = 0;
        }
    return _temp;
    }