SER_DTR
if (ISSET(bits, SER_DTR)) {
SET(rbits, SER_DTR);
if (sc->sc_mcr & SER_DTR) {
sigon |= SER_DTR;
if (sigon & SER_DTR) {
sc->sc_mcr |= SER_DTR;
if (sigoff & SER_DTR) {
sc->sc_mcr &= ~SER_DTR;
onoff = (sc->sc_mcr & SER_DTR) ? 1 : 0;
ucom_modem(tp, 0, SER_DTR);
ucom_modem(sc->sc_tty, SER_DTR | SER_RTS, 0);
#define SER_DDTR SER_DELTA(SER_DTR)