mf_udr
sc->sc_rbuf[put] = MFP->mf_udr;
rsr = MFP->mf_udr;
MFP->mf_udr = *sc->sc_tba;
c = MFP->mf_udr;
c = MFP->mf_udr;
MFP->mf_udr = c;
tmp = MFP->mf_udr;
MFP->mf_udr = *sc->sc_tba;