[ On Saturday, May 4, 2002 at 20:40:38 (-0700), Don Yuniskis wrote: ]
> Subject: Re: SparcStation ipx versus Sparc Classic
>
> > "Greg A. Woods" <woods@weird.com> wrote:
> >
> > because sun fixed their serial port design?
> 
> Ah, does that mean it was BROKEN?  Gee, all this talk about the
> "external devices" being at fault...   :>

Well, maybe, partly.  I don't know for certain what line receivers are
in what versions of the Sun systems....

> > > (ie. and how do we mimic the behavior)
> >
> > replace the RS-232 drivers on your motherboard and use only "approved"
> > terminal devices....
> 
> I suspect folks doing this will note no change in results.  For those
> using PC's/laptops, I imagine the "solution" would be a pulldown
> on the input to the driver -- since it is undoubtedly being driven
> from a Combo and floats until the Combo is configured by the
> BIOS.

That's what that resistor is designed to do....  Are you sure you
experimented with various values?

Of course there's not much you can do if a device generates an
intentional BREAK condition when it comes online, or has line drivers so
poorly designed that they simulate a real-looking BREAK condition one
one power transition or both.....  Only a really good RS-232 analyzer
might stand a chance of differentiating between these two too....

> > (and at least make sure if your machine is a model with selectable
> > signal levels that you've selected true RS-232 levels....)
> 
> Done when I first prepped the box for service...  give me *some*
> credit!  :>

Just checking!  ;-)

My little RS232 bible (*) is old enough to be rather out-of-date w.r.t.
available technology for even Sun-3s, but it's new enough to decry IBMs
stupid use of the 75154 instead of the "industry standard" MC1489.  If
Sun did anything similar on their older machines than they've definitely
made the situation worse (by more than doubling the sensitivity of
(IIRC IBM's mistake was so widely copied it became a standard: RS-423-B,
well maybe that's a bit of an exaggeration, but...)

I trust you have by now encoutered "The Greater Scroll of Console
Knowledge":

	http://www.conserver.com/consoles/

And also Celeste Stokely's Unix Serial Port Resources:

	http://www.stokely.com/unix.serial.port.resources/

On the latter page you'll find a lind to Sun-specific details which
mention that in at least some models of Sun systems there's a little
jumper to select between them:

   Port voltage:  Many Sun cpu serial ports can be configured as either
   RS-232 (+/- 12V) or RS-423 (+/- 5V).  Defaults vary.  See the
   hardware documentation for your machine to locate the jumper to
   configure this, if it exists.  Most implementations do not have to
   worry about the voltage on the serial port.

Of course in many environments the incorrect choice (i.e. 423) will lead
to more unintended "BREAK" conditions being sensed.....


(*) "RS-232 Simplified:  Everything you need to know about connecting
and interfacing and troubleshooting peripheral devices", by Byron
W. Putman, 1987, Prentice Hall, ISBN 0-13-783499-3.
-- 
								Greg A. Woods

+1 416 218-0098;  <gwoods@acm.org>;  <g.a.woods@ieee.org>;  <woods@robohack.ca>
Planix, Inc. <woods@planix.com>; VE3TCP; Secrets of the Weird <woods@weird.com>