
This is everything I presently know about ARCnet cabling, presented here
because many of you are probably like me and without an ARCnet manual.

NOTE:  Please, if you have any useful information about ARCnet cabling
       that is not mentioned here, send it to:
                       apenwarr@foxnet.net

I only have two ARCnet cards, wired together by a simple coax cable with no
terminators or anything at all.  I haven't tried any setup but my own.  Use
this information at your own risk, but think about it first.

(Oh, and if anyone wants to rewrite this into a slightly more _coherent_
mess than it already is, feel free.)

                                  -- Avery



From: "Stephen A. Wood" <saw@hallc1.cebaf.gov>
Date: Sun, 23 Oct 94 15:32:29 -0400

Here is my guess about how to wire ARCNET networks.  ARCnet seems to want to
use 90 ohm cable (as opposed to 50 ohm for ethernet).  Also, ARCnet cards
appear to have an input impedance of 90 ohms (as opposed to infinite for
ethernet.)  Therefore, the cable is plugged directly into the card rather than
using a T with either another cable segment or a terminator on the other side.
It would thus seem that an ARCnet network can only consist of two nodes.  When
I bought my two cards at a garage sale, they came with little box with four
BNC connectors on the outside.  The shields of the four connectors are all
grounded together, and the center conductors were connected by the following
resistor network.

              |
              |
              R
              |
         ---R-+-R---
              | 
              R
              |
              |

Where R is 47 Ohms.  A little math shows that if you terminate three of the
outputs with 90 ohms (A cable or a terminator), the remaining input see's
90 ohms.  Therefore this box is impedance matched to 90 ohm cable.  So this
box can be used to connect 2 to 4 nodes together.  Perhaps this box should
even be used when only two nodes are in use so that cards to see too much
signal from the other card??

Clearly one could daisy chain such splitter boxes together, although one would
quickly lose signal.  So perhaps amplifiers are needed if more than 4 nodes
are to be used.

---------------------------------------------------------
Stephen A. Wood				       CEBAF/SURA
Internet: saw@cebaf.gov                            MS 12H
Bitnet:   saw@cebaf                12000 Jefferson Avenue
                                   Newport News, VA 23606



From: jmorriso@bogomips.ee.ubc.ca (John Paul Morrison)
Date: Fri, 28 Oct 1994 23:33:08 -0800 (PDT)

The "little box with four BNC connectors on the outside" is an Arcnet
passive hub. They're worth about $5 (just so you don't get ripped
off).

I don't have specs at my fingertips. Basically, don't use too many
passive hubs (or none at all, apparently passive hubs are A Bad Thing.
On the other hand, they're a really cheap way to do things.)

Arcnet active hubs are available, they are analogous to Ethernet
twisted pair hubs. You can plug either a single station or a passive
hub into each port on the active hub. If you plug in a passive hub,
that lets you connect three more stations.

The maximum distance between two stations is 600 m or
300 m to a hub (probably to an active hub).

I don't know what the ET1 and ET2 are for, but I've heard that some
arcnet cards can be configured for longer distances; maybe that's what
those jumpers do, but I'm just speculating.

The coax cable used is RG62.

Some Arcnet cards can use twisted pair; they have two RJ11 jacks, and
jumpers to select between twisted pair and coax.  I don't know much
about this configuration. I think you run twisted pair between each
station in a ring like topology. I don't know how they are terminated,
but I have seen RJ11 terminators along with the cards, so they must
need to be terminated.

---------------------------------------------------------------------------
BogoMIPS Research Labs  --  bogosity research & simulation  --  VE7JPM  -- 
jmorriso@bogomips.ee.ubc.ca ve7jpm@ve7jpm.ampr.org jmorriso@ve7ubc.ampr.org
---------------------------------------------------------------------------



From: jojo@repas.de (Joachim)
Subject: Re: Arcnet cards

Some word on cableing. You don't need 90 Ohm cable. The following cables are
valid for arcnet:

RG-62  93 Ohm  up to 610 m
RG-59/U 75 Ohm up to 457 m
RG-11/U 75 Ohm up to 533 m
IBM Typ 1 150 Ohm up to 200 m
IBM Typ 3 100 Ohm up to 100 m

So normaly you can use you TV antenna cable (75 Ohm) for short distances.

Greetings from Dreieich
---------------------------------------------
repas GmbH          |  Joachim Koenig
Voltastr. 8         |  jojo@repas.de
63303 Dreieich      |  Phone +49-6103-390877
Germany             |  FAX   +49-6103-390810



From: Vojtech Pavlik <vpav4328@Diana.troja.mff.cuni.cz>
Date: Thu, 15 Jun 1995 16:46:07 +0100 (GMT+0100)

On Fri, 9 Jun 1995, Avery Pennarun wrote:

[...]

AP> BUS cards use terminators and T-connectors.  As far as I know, you can't
AP> connect the two types together.

I can! All that I need is to terminate the end with a STAR card. I 
think I can even connect the cards like this:

STAR------T-----T-----STAR
	 BUS   BUS

Where "-" stands for coax, "T" for T connector, "STAR" for star-type 
arcnet card and BUS for bus-type arcnet cards. I think there will be 
no terminators necessary.

[...]



From: Vojtech Pavlik <vpav4328@Diana.troja.mff.cuni.cz>
Date: Fri, 16 Jun 1995 23:46:58 +0100 (GMT+0100)


[...]
 
Thank you for this scheme! But I think the arcnet should have a 93 ohm 
cable, but the three ohms make no difference ...
 
And in my manual (I have only one for the 7 completely different 
cards) is stated that there must not be more than one passive hub 
between tro active ends (an active end is a card or an active hub),
what wasn't clear from the part of the README ...

[...]
 
Maybe you should include it in the linux kernel also .... and maybe 
all in one file sequentially - first global readme, then the wires and 
then jumpers ...
 
[...]
 
Well, when I read it now I see I was pretty unclear about this. When I 
said thet I have to terminate the end with a BUS card I was talking 
about this connection:
 
R-T----------STAR
 BUS
 
In clearer words: I have to terminate the end where is the bus card 
using a terminator. ("R" - terminator, "T" - T connector "-" - coax, 
everything other is probably clear)
 
I could also say, that I can terminate both (or only one end) of the 
bus USING a BUS card. That would best fit the picture and that is what 
you right understood.
 
And _MAYBE_ you can do even more complicated and insane combinations 
when just thinking of the STAR card as a BUS one with an inside 
installed terminator. (STAR cards are NOT bus ones with terminator, 
but I believe that they electrically act like them). 
 
[...]
 
When you have really short cables (about four meters in total) and have lack
of terminators or T's you can leave one of the terminators out .... or put
it in the middle like this:
 
BUS-----T-----BUS
        R
 
It's ugly, but it works.



