RTS
uchar_t mcr = DTR | RTS;
OUTB(MCR, RTS|OUT2);
OUTB(MCR, DTR|RTS|OUT2);
if (mcr_r & RTS)
b |= RTS;
flag = (async->async_flags & ASYNC_HW_IN_FLOW) ? 0 : RTS;
if (((mcr ^ flag) & RTS) != 0) {
OUTB(MCR, (mcr ^ RTS));
OUTB(MCR, (DTR | RTS| OUT2));