Lpc2000

________________________________

Von: Karl Olsen [mailto:kro@...] 
Gesendet: Montag, 6. Februar 2006 10:30
An: lpc2000@yahoogroups.com
Betreff: [lpc2000] Re: Rise and fall time of capture inputs

 
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.

[MEH]  This is an interesting fact. Thank you.
 
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.

[MEH]  That's the reason my signal is so slow. It's filtered with an
EMI-Filter, so no flicker should be on the line.

Karl Olsen







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[Non-text portions of this message have been removed]

Huber Martin wrote:

> 
>
>________________________________
>
>Von: Karl Olsen [mailto:kro@...] 
>Gesendet: Montag, 6. Februar 2006 10:30
>An: lpc2000@yahoogroups.com
>Betreff: [lpc2000] Re: Rise and fall time of capture inputs
>
> 
>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.
>
>[MEH]  This is an interesting fact. Thank you.
> 
>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.
>
>[MEH]  That's the reason my signal is so slow. It's filtered with an
>EMI-Filter, so no flicker should be on the line.
>
>  
>
How stable and quiet is your ground between the two units?  Ground shift 
can also occur between unit introducing "noise"?  Just a FWIW to name 
another thing that has bitten me in the past...

Regards,

TomW

>
>  
>


-- 
Tom Walsh - WN3L - Embedded Systems Consultant
http://openhardware.net, http://cyberiansoftware.com
"Windows? No thanks, I have work to do..."
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