On Mon, 30 Oct 2000, David VanHorn wrote:

> >
> >
> >Mabe I'm missing something...  but why would negative-going levels be
> >important other than meeting the letter of the RS232 electrical spec?  I
> >thought it wuld be a major deal for interoperability, but I have yet to
> >see an RS232 receiveer that won't see, say, .4V or below (usually .7 or
> >even higher) as a valid LOW signal.  Even the old ones.  Is there a large
> >base of devices not using the receiveers I'm looking at (MC148x, MAX2xx,
> >etc) or does it make a difference over longer cables?  Noise immunity? I'm
> >not disagreeing with your statement, just trying to figure out why to
> >agree with it...  8-)
>
>
> Even the ancient 1488/89 dosen't use negative levels on the receiver.
> The receiver simply counts everything below about 2V as a 1.
> (5V is a zero)

I know...  that was one of the higher cutoffs.  I think the lowest was
0.7V.  What I meant was that I've looked at the MAX and MAX-like devices
as well as the 148x and none seem to require a negative voltage fo MARK,
which was why I was wondering why I should bother.

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
                -- Isaac Asimov

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