On Fri, 14 Apr 2000 mcmahill@mtl.mit.edu wrote:

> 
> 
> 
> 
> On Fri, 14 Apr 2000, Jon Lindgren wrote:
> 
> > What happens when a serial console is disconnected from a running 1.4.x
> > machine?  I've a few sparcs which will be running 1.4.1 or 1.4.2, however,
> > I've only one vt420 :-( so I'll have to use a serial switch or
> > equiv.  I've seen messages from people before (perhaps not on this port,
> > sorry, can't remember) regarding halting the system when the serial
> > console is removed.
> 
> yes, you can halt the system this way.  I have a couple of sparc 2's in my
> lab connected with an A/B switch.  I made a minor modification to the
> switch which consisted of adding a  couple of pullup resistors.  This
> fixed the halting problem.  I'll retrieve the schematic next time I'm
> there (in a few days), and forward to the list.  I got the info off the
> web somewhere originally, just don't recall where.
> 


ok, got my officemate to read my notes on the box.

I took the A/B switch apart and on each of the "A" and "B" DB-25
connectors I added a 4.7k resistor between pins 3 and 25.

looks like I got this from:
http://www.sunhelp.org/faq/sunref2.html


In addition, since I needed a null modem, I did the following pin swaps on
the "common" DB-25 connector.
2 <-> 3
4 <-> 5
6,8 <-> 20

This seems to work ok for me.  I don't recall which terminal I'm using.
Some semi-generic serial terminal.

Hope this helps

--Dan