Lpc2000

At 05:01 PM 4/29/05 +0200, Richard Duits wrote:
>If you want to know when a falling or rising edge occurs the timer
>capture function copies to timer counter to the capture register when
>the edge is detected. If you use an interrupt to read the timer counter,
>you get the timer counter at the moment the timer counter is read and
>not the timer counter when the edge was detected. So when you read TC in
>the interrupt, the value is edge time + interrupt latency. If you read
>the capture register, it is always the edge time.
>
>This works only for edge sensitive external interrupts and not for level
>sensitive or internal interrupts. You would also need to connect the
>external signal to a timer capture pin for this to work.
>
>
>Richard.
>
>
>Robert Adsett wrote:
>
> > At 08:56 AM 4/29/05 +0200, Richard Duits wrote:
> > >Hello Jase,
> > >
> > >I would suggest to use a capture pin on timer 0 or timer 1 to capture
> > >the falling edge. This is more accurate because it eliminates the
> > >interrupt lattency.
> >
> > Umm, how does
> >
> > interrupt_occurred_at = timer_value;
> >
> > have any less latency than
> >
> > portset = 0x20;
> >
> > ??

Methinks we are answering different questions.  That doesn't measure the 
interrupt response.  That measures the pulse.  Likewise toggling an 
external pin doesn't measure the pulse it measures the interrupt response.

I think the original question was how to measure the interrupt response 
characteristics.

Robert

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