Date   : Tue, 13 Sep 2005 19:38:28 +0100 (BST)
From   : Pete Turnbull <pete@...>
Subject: Re: 2nd processor fault finding

On Sep 13 2005, 16:31, Rob wrote:

> OK I was lucky enough to pick up a 6502 second processor off ebay.
 It came
> as a board only; no PSU or cables.
>
> My problem is I can;t get it to work... I've made a ribbon by cutting
down
> an old 40 conductor IDE cable, but when the board is connected to the
beeb,
> it locks up.

That's suspicious.  As others have pointed out, the cable connects
almost solely to the Tube ULA (and ground, and power if certain jumpers
are set in a certain way, and possibly the NMI or INT -- I don't
remember about that for sure).  However, on 6502 2nd processors, the
original ribbon cable was normally fitted to a transition connector
which is soldered to the 2nd processor PCB -- it's not removable.  If
this one had no cable, presumably it has a 40-pin PCB header that has
been fitted instead.  I wonder if this has been fitted the wrong way
round?  If it has a keyway, and you're putting the cable in with pin 1
going to pin 40 (and vice versa) that would produce the symptoms you
describe.

Looking at the naked 6502 2P in front of me, with the 40-pin transition
connector labelled PL1 at the right, pin 1, with the red stripe, is the
pin at bottom right, near a tag labelled "SCN".  Pin 40 is at top right
near LK1.  The ribbon cable wants to be no more than about 8" long, and
the connector that goes into the Beeb has pin 1 on the right side as
you look at the Tube from in front of the Beeb.


-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York