Subject: Re: SparcStation ipx versus Sparc Classic
To: NetBSD/sparc Discussion List <port-sparc@NetBSD.ORG>
From: Don Yuniskis <auryn@GCI-Net.com>
List: port-sparc
Date: 05/02/2002 16:37:41
> "Greg A. Woods" <woods@weird.com> wrote:


> [ On Thursday, May 2, 2002 at 15:28:49 (-0700), Don Yuniskis wrote: ]
> > Subject: Re: SparcStation ipx versus Sparc Classic
> >
> > The damn "BREAK" detect makes this problematic for me.
>
> If you're willing to modify/replace the BBSRAM modules then surely
> you're not going to baulk at adding a little resistor to the console
> port!  :-)
>
> You can even do it on the inside of each machine to make it permanent.

And, if you think about it, this solution DOESN'T WORK!

It prevents an "open" input from glitching to SPACE and, thus, making the
BREAK.
However, the output impedance of (classic) EIA232 drivers is ~600 ohms.
So, if the external device *drives* the line to SPACE, the resistor may as
well be
sitting in your desk drawer... it isn't going to *do* anything!

So, you have to unplug the cable before applying power to the external
device
as well as before removing power from said device -- since in either case it
can "decide" to drive the line to SPACE while it is in transition.

The "right" solution is to use devices that are well-behaved and/or that
deliberately drive their outputs to high impedance during this transition
time.
The "open" / undriven input, if designed to specifications, won't "see"
a SPACE-ing condition in this case.

> -------- from the conserver distribution --------
> # $Id: Sun-serial,v 2.1 93/02/09 11:45:12 ldv Exp $
>
> If you are going to be hooking Sun consoles to your console server, you
> will run into a problem:  The sun will halt whenever the cable is
unplugged.
> It will also halt when the the console server is powered off and on.  To
> prevent this we modified the wiring of our serial cables at the end that
> attaches to the suns.
>
> The server can still be halted by generating a software line break, which
> is can be done by sending an escape sequence to the console server.
>
> WE WILL NOT BE HELD RESPONSIBLE FOR ANY DAMAGES CAUSED BY ATTEMPTING A
> PARTIAL OR COMPLETE IMPLEMENTATION OF THIS MODIFICATION.
> "WE" refers to The Ohio State University and
> specifically, the employees of CIS Department of Ohio State.
>
> This is a diagram of the cable we use.
>
> Sun file                                                     Console
> Server                                                       Server
> Side                                                         Side
>
>
>    2  Tx  -------------------------  ------------------------- 2 Tx
>                                    \/
>                                    /\
>    3  Rx  ------+------------------  ------------------------- 3 Rx
>                 |
>                 Z    4.7K resistor
>                 |
>   25  -5v ------+                                             25 -5v
>
>    7  GND ---------------------------------------------------- 7 GND
>
>    4  RTS --+                                                  4 RTS
>             |
>    5  CTS --+                                                  5 CTS
>
>    6  DSR --+                                                  6 DSR
>             |
>   20  DTR --+                                                 20 DTR
>
> I'm not a hardware person, but I think the important part is adding the
> resistor.  The rest is icing, more or less.