keithl@loop.UUCP (Keith Lofstrom) (11/23/89)
Ethernet taps connect back to the computer over 15 pin cables,
which contain 3 signal pairs: Transmit, Receive, and Collision.
You can't just swap Transmit and Receive; many computers expect to
see their own transmit signal coming back, and other computers
want a "collision heartbeat" at the end of the packet. This is
a fiendish conspiracy on the part of the tap makers, of course :-).
A) If you want a simple ethernet tap, you can use either the Intel
82C502 or the National DP8292 ethernet tap ICs. These are spendy
little devils (approx $50), but schematics for taps are given in
the data books.
B) I have a design for a multitap box that we built a dozen copies of
for a local Unix user's group. A PC board has been made, and
a local sheet metal shop has an NC tape. Kludgy design, but it will
talk to four machines, and a thinwire ethernet, for a parts cost of
about $150. It hasn't been tested on a busy network, and it probably
violates spec, but it has worked fine for us.
I'm looking for a volunteer, who:
1) Has some from-scratch electronics construction experience.
2) can do some design reconstruction from poor documentation.
3) is willing to work up and sell parts kits to others, at no profit.
If you want to make a profit, so do I, but I don't think the
design is commercial quality yet.
4) will shield me from users, and not bother me with questions that
a smart person can figure out on their own.
I guess what I'm getting at is that I've done it, got it working, helped
others make them, lost money and time, and am bored with it. If you want
just one, without all the work, buy some TCL taps, or see item A above.
If you want to devote a lot of time and effort helping others make the
boxes as a group, send some email. I will nominate a successor based on
who will help the most people for the least effort on my part.
--
Keith Lofstrom keithl@loop tektronix!psueea!qiclab!loop!keithl
Launch Loop, P.O. Box 1538, Portland, Oregon 97207 (503)-628-3645