Lpc2000

Hi TomW
 
I think you have right, but I'm interesting where the limits are.
Philips must have limits in fall and rise time but I can't find them in
any datasheets. In my opinion this are important datas for developers in
hardware.
 
Best regards
Martin
 

________________________________

Von: Tom Walsh [mailto:tom@...] 
Gesendet: Freitag, 3. Februar 2006 16:20
An: lpc2000@yahoogroups.com
Betreff: Re: [lpc2000] Rise and fall time of capture inputs


widescreen03608 wrote:

>Hi all,
>
>On the CAP0.3 input I have pulses from an encoder and I want detect
>both edges and generate interrupts. The signal is filtered so the rise
>and fall time are slow (don't know exactly how long, but surely within
>1ms). Is it possible that no interrupt is generated on CAP0.3, because
>the signal is to slow?
>
>I didn't found any datasheets from Philips which this is described.
>
>  
>
Aside from the datasheet thing, wouldn't it be possible to use a schmidt

gate to drive the capture intput?  Or some op-amp crossing-detector with

hysteresis?

Regards,

TomW



>Thanks for help
>
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> 
>Yahoo! Groups Links
>
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>  
>


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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[Non-text portions of this message have been removed]

--- In lpc2000@yahoogroups.com, "Huber Martin" <martinhuber@...> wrote:

> I think you have right, but I'm interesting where the limits are.
> Philips must have limits in fall and rise time but I can't find
> them in any datasheets. In my opinion this are important datas for
> developers in hardware.

I don't think it is possible to miss a capture event because of slow 
rise/fall times.  You get a capture event when the input is e.g. low at 
one pclk edge and high at the next, and this will happen at least once 
no matter how slow the input rises.

Another problem might be noise on the input so that you get multiple 
rise and fall events around the switching level.  The datasheets say 
that there is a hysteresis of typically 0.4V on all standard port pins 
and some more on the I2C pins, so this should filter most noise.

Karl Olsen