Date   : Tue, 30 Sep 2003 23:56:35 +0100
From   : Andrew Hancock <Andrew.Hancock@...>
Subject: Re: BBC Micro lazy delayed boot!

Thanks to Pete Turnbull on this list I've got a logic probe. So I can start
probing around the motherboard having a look at various logic states.

With 8271 chip installed.

So far, many contributors have stated check 

1. Outputs of IC 16

IC 16 555 Output 

Pin 3 (input to IC 33) RST Transitions from high to low very quickly.
Stays LOW

IC 33 74LS04

Pin 3 Transitions from high to low very quickly.
Pin 4 (output) (bar) RST Transitions from low to high very quickly. Stays
HIGH.

IC 1 6502

Pin 4 High to Low at power-on, then High with pulses of low > 30ns
Pin 6 NMI PERMANENTLY HIGH. No transition observed.



WITHOUT 8271 installed.

As above.

Except IC 1 6502

Pin 6 NMI PERMANENTLY LOW No transition observed.

I'm not too sure if I've mentioned this previously but with the 8271 chip
installed, the 15 second delay only occurs, when the DNFS 1.2 rom is
installed.

So it's a combination of both 8271 & DNFS 1.2 rom, that causes the delay.

Any ideas, where else should I stick my logic probe!

Regards

Andrew 

PS it's also hard work reading the motherboard circuit diagram on an A4
sheet!

> -----Original Message-----
> From: Sprow [mailto:info@...]
> Sent: 28 September 2003 19:46
> To: 'bbc-micro@...'
> Subject: Re: [BBC-Micro] BBC Micro lazy delayed boot!
> 
> In article
> <6A4F555CEA3CD5118DBD0002E30AC0912C0838@...>,
>    Andrew Hancock <Andrew.Hancock@...> wrote:
> 
> [snip]
> 
> > The problem still exist, I think I'll have to start checking logic
> states
> > nNMI and nIRQ lines on the CPU with a logic probe and output of IC16 and
> > IC33,giving the huge ceramic disc capacitor a wiggle as Sprow suggested.
> >
> > Which huge ceramic disc capacitor?
> 
> The one just next to IC16 (a 555).There are two actually,but only one
> governs the reset pulse width.
> 
> > And how do I proceed with checking checking logic states nNMI and nIRQ
> > lines on the CPU with a logic probe and output of IC16 and IC33?
> >
> > Apart from first I'll have to purchase a logic probe!
> 
> Just an LED connected via a spare gate will do,or looking on a scope set
> to
> 1V/cm vertical.
> 
> I'm a little puzzled how DFS 0.90 and DFS 1.20 are different,particularly
> if
> there's no NFS chip fitted,as NFS also has an intimate relationship with
> nNMI,
> Sprow.