TMOD = (TMOD & 0xF0) | 0x01;  /* Set T/C0 Mode */
  CKCON = (CKCON & ~0x03);      /* Select external oscillator as source */
  CKMOD = (CKMOD & ~0x03);      /* Select external oscillator as source */
  TMOD = (TMOD & ~0x02);        /* Select external oscillator as source */