Date   : Tue, 12 May 2009 09:18:09 +0100
From   : mike@... (Mike Tomlinson)
Subject: BBC B+ Econet weirdness

In article <4A08751A.5060405@...>, Michael Firth
<mfirth@...> writes

>When the machine is powered on, there is about a 50% chance that it 
>won't communicate on the Econet. Any Econet commands will just hang 
>indefinitely.

How long have you waited?

>Until today, its been working fine, with both NFS 3.60 and ANFS 4.18.

Is the Econet interface a factory fit or a later addition?  The kits
supplied by Acorn were tricky to fit due to the confusing colour-coding
of the resistors and the tightness of space on the main board (making it
necessary to be very sure where you were fitting components).

Getting the fitting wrong, especially confusing resistor values, could
result in all sorts of wierd behaviour.

>Has anyone seen a similar behaviour on an Econet machine before?

Yes, as above.
>

>Also, does anyone know how the 'collision detectless' operation works - 
>the B+ hardware doesn't have the second LM319 fitted, but as far as I 
>know is designed to work with the standard NFS 3.60, which was written 
>before the B+ was designed?

I seem to remember that the B does do collision detection, but it's not
done with the second LM319.  It's done another way.  Would need to look
at the cct diagram.

Some (not sure if all) the missing circuitry on the B interface was to
do with clock generation, wasn't it?  This was before Acorn decided to
go with the separate, central clock box.

>Finally, does anyone know if there's anything special that would need to 
>be done to upgrade the machine to support hardware collision detect, 
>beyond adding the second LM319 and passive components listed as 'NF' on 
>the B+ schematic?

As above, I'm nearly sure it's already present on the B, just done in a
different way.

The Master modules came in 4-chip (no collision detect) and 6-chip
(collision detect) versions.  The 4-chip models were abandoned by Acorn
and replaced with 6-chip under warranty.

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