> 
> > On Thu, 12 Jun 1997 10:29:02 -0700,
> > Um, don't Macs use RS-422 for their serial ports instead of RS-232?
> > RS-422 signals are differential but IIRC, only RD and TD signals are
> > actually differential and the rest are single-ended in Mac's serial
> > ports.  For the rest, the negative pins of diff. receivers are simply
> > grounded and only the positive pins are used.
> 
> Hmm.. I'm not sure I would believe that.. Since I've got an external RS232
> modem connected at home to my IIci with a plain-jane serial cable.. Unless
> I'm mistaken, RS422 is not compatible with RS232 without some sort of converter
> box..?
> 
> I'm sure someone out there knows this for sure..

No, the ports are RS-422. But if you throw away TRx+, and tie TRx- to TxD,
and tie RxD to Rx- & Rx+ to Ground, you can move between the two.

Take care,

Bill