void keypad_init (void)
{
  // define pattern
  KBPATN = 0x4E;
  // define P0 pins that trigger interrupt
  KBMASK = 0x4E; 
  // pattern must not match
  KBCON = 0x00;

  // set P0 pins as inputs
  //P0M1 |= 0x4E;
  //P0M2 &= ~0x4E;

  // set isr priority to 0
  IP1 &= 0xFD;
  IP1H &= 0xFD;

  // enable keypad interrupt
  EKBI = 1;
}