Sun 3 console question

[Paul Allen]

In article <20329 at lll-winken.LLNL.GOV> casey at lll-crg.llnl.gov (Casey Leedom) writes:
>erickson at frith.egr.msu.edu (Carl B. Erickson):
>> Can someone point me to the fix that has been discussed for using a
>> terminal as the console on a Sun 3?  I believe this involved a small
>> circuit of some sort.
>
> [Casey describes a problem with his RS232 Sun consoles hanging]
>Is this the problem that Carl was referring to above?  And if so, is there
>indeed a fix???  I had resigned myself that Sun just didn't know how to
>design an RS232 interface.

I think there are two problems here.  One of my 3/280's has a VT220 as its
console.  Once in a blue moon, I've seen it hang like Casey describes.
It's never bothered me enough to spend time tracking it down.  If anybody
has a fix for this, I'm mildly interested.  :-)

I believe the circuit that Carl referred to is a kluge to prevent DTR from
dropping when you unplug (or power off) the console terminal.  Without
such a circuit, unplugging the console results in a watchdog reset.  As I
recall, the circuit involved a single transistor and allowed the break key
to reset the processor while preventing DTR from dropping if the terminal
was accidentally unplugged or turned off.  I remember seeing a posting
describing this circuit, but I can't find any trace of it in my archives.
Did anybody else save a copy?

Paul Allen
pallen at atc.boeing.com

Paul L. Allen                       | pallen at atc.boeing.com
Boeing Advanced Technology Center   | ...!uw-beaver!ssc-vax!bcsaic!pallen