Lpc2000

Gus,
Why dont you just gate the incoming frequency with a pwm/timer output which
generates an interrupt also when it goes "off" (could be clock tic from ur
RTOS) and with the larger collection of  cycles each millisecond (say) ur
accuracy can be limited only by ur PCLK frequency. The ISR should just read
the timer and reset it allowing the CAP a fresh start and background process
ur calcs for the frequency. You can make it easy by selecting a suitable
PCLK frequency also.
Good grief Charlie Brown!
Rgds
DonW

----- Original Message ----- 
From: "Gus" <gus_is_working@...>
To: <lpc2000@yahoogroups.com>
Sent: Tuesday, August 09, 2005 10:56 PM
Subject: [lpc2000] Re: measuring pulse width


> >From what you guys are saying, I think my ISR is too slow!! When I
> feed my system with 10KHz 50% duty, I get 10% error around the
> correct value
> In my ISR, I mesure the pulse width by subtracting the last timer
> count from the current timer count.
>
> Any suggestions?
> On an average, how many interrupts/second can the LPC handle?
> On 10KHz with 8 cpture channels, I get 160,000 interrupts per
> second. Is this possible?
>
> Gus
>
> --- In lpc2000@yahoogroups.com, "philips_apps" <philips_apps@y...>
> wrote:
> > Hello Gus,
> >
> > LPC2000 samples every CAPx.y input in use at the rate of pclk. It
> > takes two consecutive CAPx.y samples for a transition to be
> detected
> > (i.e. if the current CAPx.y sample is high and the previous sample
> > was low, CAPx.y recognizes a rising edge).
> >
> > Assuming no jitter in the processed incoming signal and no jitter
> in
> > the cclk/pclk clock, consecutive readings of the CAPx.y register
> > content should not vary for more than 2 ticks in the worst case.
> The
> > first uncertainty tick comes from the detection of the pulse's
> > leading edge, and the second uncertainty tick comes from the
> > detection of the pulse's trailing edge.
> >
> > What is the duty cycle of the signal you are processing? Do you
> use
> > the same capture input to detect both rising and falling edge or
> you
> > have two dedicated capture configured pins?
> >
> > Regards,
> >
> > Philips Apps Team
> >
> >
> >
> > --- In lpc2000@yahoogroups.com, "Gus" <gus_is_working@y...> wrote:
> > > Hello,
> > >
> > > What is the shortest pulse you can mesure on LPC capture module?
> > >
> > > I am trying to measure some pulses using the capture hardware on
> > LPC
> > > chips. The processor is running at 48Mhz and my capture module
> is
> > > running at 1us/ticks
> > >
> > > Connecting a function generator, I can read valid results up to
> > 1Khz.
> > > When I go over 10KHz, the reading is not stable at all! About 10%
> > up
> > > and down.
> > >
> > > Thanks,
> > >
> > > Gus
>
>
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>
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