If the key is so poor that it has more than a 10ms bounce, then perhaps
the time constant of the test needs to be increased. The routine itself
is bulletproof using the pattern b'11110000', indicating that it was low
for 4 cycles then was high for 4 cycles.

--Bob

Michael Rigby-Jones wrote:

>>-----Original Message-----
>>From: Bob Axtell [mailto:cr_axtell@YAHOO.COM]
>>Sent: 18 June 2004 18:59
>>To: PICLIST@MITVMA.MIT.EDU
>>Subject: Re: [PIC]: anding/masking {handling keys}
>>
>>About 10 years ago I began using a bulletproof way to process keys:
>>
>>1. I read the keys- all of them- every 10ms or so. I can
>>either read 'em all at one tome, or rotate so that I read each
>>one on a rotating basis. Doesn't matter how its done, it works
>>perfectly regardless.
>>
>>2. Every 10ms I read the key and shift its value into a
>>register decicated just for that application.
>>
>>3. If the key is ZERO when it is pressed, I look for the
>>pattern b'11110000' on that key's register. When that is seen,
>>that key was PRESSED AND RELEASED, so set a flag. To prevent
>>more action, jam the key's register with '11111111' so it
>>can't be used again.
>
>
> I'm not convinced of the "bulletproofness" of this technique.  If the switch
> in question has a bounce time of more than 10ms (which isn't uncommon), you
> may never get the exact bit pattern you are looking for, and the keypress
> would never be registered.
>
> Regards
>
> Mike
>
>
>
>
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--

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         Bob Axtell
PIC Hardware & Firmware Dev
   http://beam.to/baxtell
       1-520-219-2363

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