Lpc2000

> If this is indeed correct, the big question is - do I have to use an
> external watchdog after all and what level of protection / garantie
> am I getting from the internal one. In short - is the internal one
> of real use in a critical application?
>
> Any comments or experience??????
>
> Regards
>
> Mark Butcher

Hi Mark,

I'm personally always wary of internal watchdogs for critical

applications, if they only have 1 state with a one shot.

I always prefer an external WD with 2 states or IOW, it expects 0->1

AND 1->0 transitions.

This way ideally you set the ext. watchdog somewhere from a common

point in "foreground", and clear it from a point in say an ISR tick -

something that indicates Interrupts continue to be handled.

If either fails, you get a System reset.

Bear in mind though that with very strong field strengths such as the RF you're

testing with (900 MHz GSM I assume),

an external watchdog probably won't help either.

No CPU I think can be expected to continue correctly with these kind of fields,

if there's sufficient wiring around to pick up the stray RF, rectify it, and severely

shift DC bias all over the place. ONE wire/track attached to MCU about 8 cm long

already makes for a quarter wave "antenna".

There will of course be lots of connections to MCU, so the next thing is to be very

careful with your clock layout. Pickup there is the most disastrous.

The first step for those sort of things would be careful EMI suppression,

control of ESD getting in anywhere in the system, shielding if need be etc.

b rgds

Kris