Date   : Mon, 07 Feb 2005 11:00:15 +0000 (GMT)
From   : Chris Johns <chris.johns@...>
Subject: Re: BBC SWRAM module

On Mon, 7 Feb 2005, Michael Foot wrote:

> Quoting John Kortink <kortink@...>:

> > On Sun, 6 Feb 2005 03:12:04 +0000 (GMT), Greg Cook wrote:
> >
> > >[...]
> > >
> > >The yellow wire is sampling /R/W (SRAM mods normally take R//W from a
> > >nearer pin) but there are spare gates on the "module" to invert the
> > >signal.
> >
> > It samples NR/W nand 2MHzE, which makes for a cleaner and
> > safer write strobe, because it is then synced to the data
> > transfer part of the bus cycle, as it should be (instead
> > of relying on accidental 6502 behaviour of defaulting to
> > 'read' on R/nW).
>
> Thanks for all the info so far. I've uploaded a much better photo:
> http://homepages.paradise.net.nz/mjfoot/SRAM_2.jpg
>
> I agree that it's a homemade job and that whoever did it knew what they were
> doing. I've not seen a schemetic for this type before but it looks overly
> complex to me. The green wire going to S37 is interesting.
> Unfortunately because it is an Econet only machine, I've not go around to
> testing it out yet.

I notice the lack of (D)NFS chip in that machine - did it come like that
or did you take it out?

I can't quite make out what's under the homemade thinggy, it looks like it
could be 2 chips "stuck together" - maybe one of those is DNFS and the
other is the RAM - so the extra logic is to use both in the same socket?

I could just be wrong, of course :P

Cheers

Chris