Date   : Wed, 14 Sep 2005 19:16:33 +0100
From   : "David Hunt" <dm.hunt@...>
Subject: Re: 2nd processor fault finding

Funny, that Acorn decided to put pin 1 on the left rather than the right
like the Beeb and everything else, e.g. IDE/ATA on PCs. The IDC connector
isn't fitted backwards (you can't really do that with a right angled
connector) it's just Acorn being different! Coincidentally, the Cambridge
Co-Processor has pin one on the right hand side, the Z80, like the 6502 has
it on the left, I guess they figured it out eventually!

Dave ;)

-----Original Message-----
From: Majordomo List Manager [mailto:majordomo@...] On Behalf Of
Rob
Sent: 14 September 2005 00:43
To: BBC Micro Mailing List
Subject: Re: [BBC-Micro] 2nd processor fault finding


Many thanks for all who responded.  Pete's assessment turned out to be 
correct; the board has an IDC connector on it (the same as the ones under 
the beeb) and whilst the soldering is not obviously any different to the 
rest of the board, it IS fitted backwards compared to the description of 
Pete's cable.

After I reversed the cable (after shaving off the key on the cable mounted 
socket..) and re-seated all the chips for good measure, everything worked
fine!

I'm running it from an external 5V PSU as although I thought of trying it 
from the beeb's PSU,  the machine I want to use it with already has a full 
ATPL board, GoMMC and beeb-powered floppy drives, so I figured I might be 
already be overloading it slightly..

Jules:  Yes, on the master I got all it's normal boot up messages (OS, DFS, 
BASIC messages) and a flashing cursor, but nothing on the keyboard worked 
(not even caps lock)  The B didn't even boot.

Thanks all!!

Rob.


At 19:38 13/09/2005, Pete Turnbull wrote:

>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