Date   : Thu, 15 Sep 2005 07:36:21 +0200
From   : "Eelco Huininga" <eelco@...>
Subject: Re: 2nd processor fault finding

 

> Hi All,
>
> 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.. (specifically, a B presents no display and a 
> constant beeb, and a Master boots up fine, but locks up with no 
> keyboard input accepted.)
>
> I've tried it with the 2P powered on and off.  I've even swapped the 
> tube ULA and swapped it with the one on a Master internal 6502, and it 
> worked in there.  The odd thing is I get the same symptoms with the 
> tube ULA removed from the board, when my reading of the circuit 
> diagram indicates that nothing on the ribbon connects anywhere else!
> The ribbon alone connected to a beeb doesn't affect it at all, which I 
> would have thought it would if it were a problem with the cable.  I'm 
> presuming I only need a straight through cable..?
>
> Any clues anybody, or shall I get back onto the seller - he did 
> advertise it as working.
>
> Rob.

That's weird indeed. I think you've got a problem with either the /RST
signal, or the /IRQ signal. Check them with an oscilliscope wether they stay
low all the time.

Eelco