EIA 232 vs. 422, Color Computers (was Re: Serial floppy drives)

From: Peter C. Wallace <pcw_at_mesanet.com>
Date: Thu Sep 5 17:23:00 2002

On Thu, 5 Sep 2002, Tony Duell wrote:

> >
> > Eric Smith wrote:
> > >
> > > > <snip>
> > Connecting EIA-232 directly to EIA-422 could let the smoke
> > > out of something, and we certainly wouldn't want that.
> > >
> >
> > ISTR that 422 was simply a balanced line version of 232. I think you
> > can just tie to the non-inverting line and ground and make it work.
>
> I am _darn_ sure that the RS422 spec does not allow +/-25V to be applied
> to the receiver input. Which an RS232 driver might well do. And in fact
> there's no requirement (AFAIK) for the common mode range of the
> differential input to include ground.

Maybe the confusion occurs because one of the most common RS-422 receivers is
the 26LS32C which does have a +- 15V input range (+- 25V abs max)


>
> It may work with Apple's so-called RS422, but that is so far from real
> RS422 that I don't know how they got away with calling it that...
>
> -tony
>
>

Peter Wallace
Mesa Electronics
Received on Thu Sep 05 2002 - 17:23:00 BST