Date   : Mon, 11 May 2009 19:57:30 +0100
From   : mfirth@... (Michael Firth)
Subject: BBC B+ Econet weirdness

Hopefully someone here might have some ideas about a weird problem 
that's appeared today on my BBC B+'s Econet interface.

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.

I've probed the various pins on the 75159 driver, and that seems to be 
working - pin 9 goes active for a few seconds, and pin 11 is 
oscillating. Pins 12 and 13 are active while pin 9 is active.

After a few seconds the transmit seems to give up - pin 9 goes inactive 
and it stops driving the Econet bus. It seems to me that its failing to 
receive for some reason, but I haven't yet diagnosed what the LM319 and 
68B54 receive side is doing when it doesn't work.

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

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

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?

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?

Thanks

Michael