Thanks for sharing! Sounds like Gray code with twos complement math
to me. If you've never heard those two terms then I think you should be
justly proud in having come up with the solution on your own- it shows
insight into what's actually going on under the hood, so to speak.

Mike H.

On Tue, Oct 11, 2011 at 8:08 AM, <jim@jpes.com> wrote:

>
>  All,
>
>  I have been working with a rotary encoder that I am planning to use as
> a control for a piece of test
>  equipment at work.  I have looked on the web for algorithms to decode
> the outputs of said encoder,
>  and have found several.  Most of them work as advertised in my
> application, but I have come up with a
>  version that works very well in my opinion.
>
>  I don't know whether it is new or novel, but all I have done is watch
> for the "A" output to go high.
>  When it does, I then read the port that the encoder is attached to.  I
> mask of the bits I am interested
>  in, and use this as an index into a table.  If the value is "01" I add
> "1" to my variable.  If the value
>  is "10", I subtract "1" by adding 255.  Any other combination "00" or
> "11" adds a zero for no change.
>
>  I have tried this out spinning the knob on the encoder as fast as I
> can, and I can't see any missed
>  counts.  I am using a delay of 2.5 mS in my routine for debouncing.
>
>  If anyone is interested, I can post the code.  But my guess is I have
> just on my own rediscovered an old
>  method of decoding rotary encoders.
>
>
>  Regards,
>
>  Jim
>
>
>
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