Microvaxen bits etc. - test-drb@ccmp.vtda.org

27 Oct 1998

-----Original Message-----
From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Wednesday, 28 October 1998 14:19
Subject: Re: Microvaxen bits etc.

...
 Oh well... Another useful product becomes unavailable
thanks to progress...

Seems that way.  I may have found a source of new ones, but the price is a
bit much.
S/H ones seem to disappear as soon as they come out of service.

...
 > Most network cards produced these days don't
have AUI ports on them. 
...
 Yes, a lot of them are 10 base T only. Even though
(IMHO) 10 base 2 makes
more sense for a small home network (no need to have a hub) and BNC plugs
are a lot easier to wire than those RJ45 things. 

Oh, RJ45's are no problem provided you have a decent tool. I use crimp on
BNC's as
well.  I have a mix of both on my home network and at my shop.  The school
is all cat 5 now.

...
 Fortunately, I got a load of transceivers at a radio
rally with minor
faults (mostly open-circuit connections on the BNC connector). 

Lucky boy.

...
 If there's a 16 pin chip near the BNC connector
marked 83C92 or something
like that, then it can be made into a transceiver. You can either raid
the bits off the card or (Hey, a good idea...):
A lot of cards have 6 links that you have to move to select between AUI
and 10 base 2. They simply link the appropriate signals from the logic on
the card either to the AUI connector or to the internal transceiver. It
should be possible to feed signal from an AUI 'input' to the right pins
on those links, apply power (you probably only need the +12V line) to the
card and avoid a lot of work. 

<GRIN>   Actually, this thought also crossed my mind whilst gazing at just
such a card.
I'm going to try that.  I have an NE2000 clone card I'm going to try and
convert to a txcvr.
I think it needs +-12v and +- 5v, but that's not a big problem. (Diskless
workstation PSU)

...
 If you want to try this, then you'll need to trace
out the schematic
around the links. It's worth knowing that most of the pulse transformers
used to isolate the logic signals at the transceiver contain 3 little
transformers in a 16 pin DIL package on pins (1,2,15,16), (5,6,12,13),
(7,8,9,10). 
Yep, can see them.

...
 Trace the secondaries to the transceiver chip and then
you
know what each transformer section is for (one will be Tx Data, one
RxData, one Collision). Alternatively, trace the link connections to the
ethernet chip on the card, but it may be more difficult to get data on
that. 
Not even gonna try.  A direct patch into the txcvr from the AUI port with a
little xover cabling ought to do it.

...
  Did I mention that you'll need the data sheets on
the transceiver chip? 
You did.  Know a source?  Online one preferably?

...
 The  pinout is : <snip>

Got it, thanks for that.

...
   connect them.

The cable is special :-(. It's 4 twisted pairs + shields (which you link
to the ground pins). One of the twisted pairs is thicker than the other
3, and is used for power. 

I imagine most anything will probably work, provided the leads are kept
short.
I have some shielded audio stuff that should do nicely.
Something to experiment and tinker with for a while. :^)

Cheers

Geoff Roberts
Computer Systems Manager
Saint Marks College
Port Pirie  South Australia.
My ICQ# is 1970476
Ph. 61-411-623-978 (Mobile)
      61-8-8633-0619 (Home)
      61-8-8633-8834 (Work-Direct)
      61-8-8633-0104 (Fax)