UMCON_DTR
sc->sc_mcr_dtr = UMCON_DTR;
sc->sc_mcr_rts = UMCON_DTR;
sc->sc_mcr_dtr = UMCON_DTR | UMCON_RTS;
if (ISSET(sc->sc_umcon, UMCON_DTR))
sc->sc_umcon = UMCON_RTS|UMCON_DTR;
SET(sc->sc_umcon, UMCON_DTR);
CLR(sc->sc_umcon, UMCON_DTR);
sscombits = UMCON_DTR;
CLR(sc->sc_umcon, UMCON_DTR);