Lpc2000

At 10:12 PM 10/17/05 -0400, Landrum Haddix wrote:
> > I think the additional micro as watchdog is not a bad idea.  A little 8 
> pin
> > micro can act as quit a flexible watchdog.  1 pin for reset, 1 as the
> > watchdog input, a couple to check for various startup or runtime
> > conditions.  If it has a good reliable power monitor built in even
> > better.  It' may even be cost competitive with a windowed watchdog.
> >
> > Jack Ganselle has an article where he waxes rhapsodic about the 
> possibilities.
> >
> > Robert
>
>Robert,
>We thought of that today. There are some SOT-23 PICs with 4 I/O that
>would be cheap and perfect. Downside is they have to be programmed
>somehow. So far my design is entirely flashable from outside.

Well there is something to be said for having your watchdog be 
non-modifiable :)

>You could even speak I2C to it and schedule the next reset pulse to
>occur if there is no further comm.  This could even include as special
>value for the duration that meant disable the watchdog function.
>
>It's dissapointing however to have to use a PIC beacuse it has a
>reliable watchdog and BOR to pull reset on the ARM because it doesn't.

Well, I've always been too paranoid to rely on a micro to provide a reset 
output in the case of brownout.  A fair power monitor circuit has to 
guarantee a low out (not floating) down to a Vcc of 0.8V, a good one should 
go lower.  Especially important as supply voltages drift ever lower.

One of these days I'll sit down and satisfy myself that it can be made to 
work.  The non power side I'm convinced of.

Which raises a question for the original poster.  Do you have a power 
monitor that provides a reset when your power line goes low.  Pulses on the 
power line could give you the symptoms you see.  And given the environment 
you describe a ground bounce is not out of the question.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/