C_RS_DTR
SET(czttybits, C_RS_DTR);
CLR(sc->sc_chanctl_rs_control, C_RS_DTR | C_RS_RTS);
if (ISSET(rs_status, C_RS_DTR))
sc->sc_rs_control_dtr = C_RS_DTR;
sc->sc_chanctl_hw_flow = C_RS_DCD | C_RS_DTR;
sc->sc_rs_control_dtr = C_RS_DTR | C_RS_RTS;
if (ISSET(sc->sc_chanctl_rs_control, C_RS_DTR))