UCYCOM_DTR
SET(combits, UCYCOM_DTR);
CLR(sc->sc_mcr, UCYCOM_DTR | UCYCOM_RTS);
if (ISSET(combits, UCYCOM_DTR))
SET(sc->sc_mcr, UCYCOM_DTR);
CLR(sc->sc_mcr, UCYCOM_DTR);