Date   : Sun, 07 Mar 1999 09:33:31 +0000
From   : Mike Tomlinson <mike@...>
Subject: Re: Econet, etc.

In article <19990306203950.A1423@...>, Tom Lees
<tom@...> writes

>I think also it might
>be a Motorola chip rather than a Rockwell one.

It is.

> Does anyone have a URL
>into Motorola.com that can find datasheets. I did get there once, but
>that was from a link from a massive chips database, which I can't find
>anymore 

try http://www.xs4all.nl/~ganswijk/chipdir/

George Hawes (formerly of SJ, now working for i-cubed) produced a superb
series of training and application notes on the workings of Econet.  If
you ask him nicely, he might be willing to dig them out and send them to
you.  support@... is the address I think.

Random facts from the dregs of my memory:

Econet is a serial protocol - it basically uses the 68B54 as a glorified
serial chip - running over 4 wires and earth.  The signals are
differential, with two wires are used for data and two for the clock.
This has the advantage of negating any interference.

The speed of the LAN is set by the clock.  The clock speed is set by
jumpers and the clock should be customised to the LAN in use (this
depends on cable length, quality of installation, the machines attached,
etc.) but a typical speed is 200kHz.

Econet is a CSMA/CD protocol - Carrier Sense Multiple Access, Collision
Detect.  A station wishing to access the wire listens to it and, if it
is idle, begins transmitting.  If another station simultaneously begins
transmitting, a collision occurs and both back off and wait for a length
of time (I think based on the station number) before retrying.  The
terminators are VERY important in Econet as they raise the wire to its
idle state when no data is being transmitted - no terminators, no idle
state, no communication.

Econet uses a 4 way protocol - the sending station sends out a scout
packet, which is acknowledged by the recipient.  The data is then
transmitted and again acknowledged.  I seem to remember Acorn
experimented with a version of Econet where the acks were not required,
in order to speed things up, but it was not a success.

I have lots of notes up in the loft from Aocrn training courses, etc.
but it might be best if you can get George's notes in electronic form.
Another place to start is to read the Econet level II and level III user
guides, and the Econet Advanced User Guide, all of which I think are on
Mark's documentation project site.

If you have any more questions please post them to the list and I will
endeavour to answer them.

Mike

-- 
Mike Tomlinson
See the sci.electronics.repair FAQ mirror at  
http://www.jasper.demon.co.uk/repairfaq/