Date : Tue, 12 May 2009 09:50:30 +0100
From : michael.firth@... (michael.firth@...)
Subject: BBC B+ Econet weirdness
> -----Original Message-----
> From:
> bbc-micro-bounces+michael.firth=bt.com@...
> [mailto:bbc-micro-bounces+michael.firth=bt.com@...
.uk] On Behalf Of Mike Tomlinson
> Sent: 12 May 2009 09:18
> To: bbc-micro@...
> Subject: Re: [BBC-Micro] 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?
>
Having had a look at the B+ service manual, there is a 4.5s timeout on
attempting to send a packet, so I think if it doesn't error out before
this then the hardware will lock up.
I've certainly left it 60s+ and it doesn't return. Escape doesn't work
either, Break is needed to release the lockup.
The fact that if the machine is power cycled then there is a reasonable
chance that the Econet starts working suggests its either a silicon startup
problem, or some other power-on-reset condition not working right.
One the machine has powered up in a 'working Econet' state, the Econet seems
to stay operational until its power cycled again.
> >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.
>
This is a factory fitted interface (the PCB is actually out of an ACW).
As I said elsewhere in the message, until yesterday the machine had been
running fine on Econet for several weeks, which I think would rule out any
incorrect fitting problems (but not a component going faulty)
> >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.
>
The machine in question is a B+, not a B. The B+ has space on the
PCB for collision detection, but, quoting the service manual "the
collision detect circuitry is not fitted because the software protocols
should prevent any collision"
> 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.
>
That's true of BBC A/B machines, up to PCB Issue 3. BBC B Issue 4 and 7,
and all later Acorn user machines don't have provision for internal clock
generation or termination. (I say 'user machines', because I think the
Filestores had clock generation)
> >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.
>
Sadly the B+ Econet design dates from a similar period to the Master 4-chip
module. Fortunately, as Rob has said, and the service manual confirms, it is
possible to add the missing collision detection to the B+.
I'm not convinced that's my only problem though.
Regards
Michael