Date   : Wed, 29 Mar 2006 00:44:11 +0100
From   : Fragula <fragula@...>
Subject: Re: Model B NMI PITA.

Phil Blundell wrote:


> S2 needs to be open for Econet; S9 needs to be open for the disk
> controller.

Exactly.

 In theory at least, you just need to cut both links
Unfortunately, in practice it seems the econet stops working at just
that point.


> should be in business.  It's a bit weird that shorting S9 would make a
> difference to the Econet:

Indeedy. Just in case I got it backwards in the last message. S9 seems
to want to be Closed for the econet to work.. Cutting it (to get the FDC
NMI up) makes the econet lock up on useage. It detects clock (or
otherways) correctly, machine works fine, until any kind of access is
attempted, then it just locks forever. no "network jammed" or "not
listening", and the only way out is the One Fingered Salute.


> all it does is prevent the FDC from driving
> NMI though one gate of IC27; S2 does likewise for the ADLC using another
> gate in IC27.  Closing either of those links with the appropriate
> hardware in place will short an output from IC70 or IC91 to ground, so
> not a good idea.

Hmm. I'd assumed them to be open collector outputs against a pullup
resistor to get effectivly an OR on the NMI. Its been a while.. But at
least my beard isn't grey.. Just shaved it off!

It was either that or tear it out...


> What issue is your PCB?

Both of the ones on the table at the mo are Issue 7. One yellow screen
(came with econet) one white screen board. The white screen is Old
Faithfull, which got its econet bits soldered in way back when, and
which now I'm thinking we had to do something on the underside of the
board to make it work.. Fix a track or something that was wrong from
factory, either on a batch or on all Iss.7. But that didn't fix it either.


> The early ones, up to (and maybe including)
> issue 4, needed some extra modifications in that kind of area to make
> them work.

And I also have an Iss.4 with "Factory" econet, that I'm hoping not to
butcher. Guess an FDC doesn't really count as butchery tho.. or an ATPL
board. But neither of those have gone in yet.

> I think the service manual (which is on Mark Usher's site somewhere) has
> some words about how to perform the disk and network upgrades,

Yep. I grabbed it, in spite of having a printed one. Maybe I should go
over it again.


> including
> the link settings.  Might be worth checking that out and making sure
> you've been through all the right motions.

Yep. I'll wait for my glasses first tho.


> I have a B with both 1770 and net lurking upstairs somewhere.  I'll go
> dig it out.


I don't think the 1770 should make much difference.. The DFDC (Mk.II) is
register compatible with the Acorn 1770 when in 1770 mode. Maybe there
is something peculiar about iss.7 and I need to try the DFDC on the
Iss.4. But I don't have a (thinks) probably 7437. the IC in question is
soldered on the Iss7, but an empty socket on the Iss.4.

Dammit.. Went to Maplin today. New Nicads for the FDFS, Integra B, and
the two ATPL boards. None the right type. Also no suitable .1uF caps for
my smoked supply. (that was the yellow iss.7) Luckily I have a spare
sick supply (has a dead chopper anyway) that i stole one off, so that's
all ok. again. For now. I'll have to get an order off to Farnell.. need
some bits for my mixer (musical type, not food) too, and Farnell/CPC
seems to be the only game in town for that now. Bit of a wasted trip
really..

Except for I managed to pick up a bit of venison on the way back.

Cheers!

M.




-- 
(Sorry if I top-quote occasionally, the b@...*rds make me use LookOut in
work.)