Date   : Tue, 12 May 2009 16:27:55 +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 16:12
> To: bbc-micro@...
> Subject: Re: [BBC-Micro] BBC B+ Econet weirdness
> 
> In article 
> <89056F0D6B620444BE8677A5802EE49F081B9D5F@...
> 1.systemhost.net>, michael.firth@... writes
> 
> >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.
> 
> Possibly suggests an interrupt problem or slow/dicky RST- line. As
> you've said you have replaced the 68B54, if there's a circuit 
> on the B+
> taking INT- from the 68B54 through to the 6502 (I seem to 
> remember it's
> not straightforward), I'd be looking at that.
> 
I haven't tried replacing the 68B54 yet - it will be quite a big job,
as the only spares I have are soldered to Master Econet modules, and
the B+ chip is soldered to the PCB.

> You are sure the Econet spine is in good order and has good 
> termination?

The Econet spine seems fine - its all home made, which means its probably
not perfect, but other machines on the spine were communicating fine while
the B+ was sulking, and indeed communicating past it, suggesting the cabling
its connected to is fine. I replaced its DIN5 lead with one from another
machine, and the problem stayed with the B+.

> Does the machine still hang if you unplug the net and press 
> Break a few times?

Unfortunately the machine has been working so far today, so my further testing
has been somewhat hampered.

If I can get it to go wrong again, I'll have a look at the NMI generation, and
the RXD / CTS / RTS pins on the 68B54.

> >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)
> 
> Agreed.
> 
> >The machine in question is a B+, not a B.
> 
> Sorry, didn't read your original post properly! Hadn't had enough
> coffee...
> 
> > 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"
> 
> I'd definitely fit it.
> 
When I saw that it could be done, that was my plan. Just need to get
hold of a through-hole LM319 now...

Thanks for the advice so far.

Michael