Lpc2000

At 10:10 AM 2/8/05 +1000, Peter Jakacki wrote:

>maestral64 wrote:
>
> >My problem is that I would like to use 'faster' reset, with reset
> >delay time up to 100ms. By datasheet 2114 needs min 10 ms. For
> >Microchip circuit time delay is 140 ms min, up to 0.5 sec(!) max.
> >Any idea/recomendation? Again, I am little bit sceptical to use rC
> >circuit reset in professional stand-alone application.

<snip>

>The problem with reset chips is that they are overly expensive (why?)
>and customized. I find it cheaper to employ an 8-pin micro
>(PIC12F,LPC900)complete with power-on timer/brown-out detect etc. I can
>configure these for my reset threshold, reset time etc. These micros are
>typically stand-alone, not requiring any external circuitry such as
>crystal etc to operate.
>
>PLUS!, there is always the bonus of having it monitor the coms line and
>being able to reset or ISP the main processor as well as being able to
>operate as an independant configurable watchdog.
>
>Summary:
>Configurable intelligent watchdog/reset/monitor *costs less* than a
>fixed reset chip.


But to how low a voltage do they operate.  A good reset chip will provide a 
low output down to about 0.8V.  It would be a real problem if the 8 pin 
micro's brown-out circuitry kicked in and caused the reset line to float at 
say 1.7V.  I suppose you could reverse the problem and use a resistive 
pulldown and override that with a positive output but then you need to know 
how high a resistance you can use and still provide a reset voltage 
(particularly at low VCC), is that specced anywhere?

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