Actually, interrupt on change is just about the only way to make quad
encoding work. Set the PIC up to capture a change on both the A and
the B pins. When you get into the routine, immediately read repeatedly
until you get 3-5 SAME results on BOTH A and B. The XOR with old
state, etc as is needed. I think you will see things clear up.

--Bob

On Sat, Sep 5, 2009 at 5:58 PM, Josh Koffman<joshybear@gmail.com> wrote:
> On Sat, Sep 5, 2009 at 8:36 PM, Ray<list@microdesigns.biz> wrote:
>> Josh,
>> I was doing 4 quadrant decoding of a rotary encoder on a motor back in t=
he 70's
>> The problem is when the encoder rests on an edge instead of off 45 degre=
es.
>> On an edge the dithering =A0of +1/-1 can be very high frequency in X4 mo=
de.
>> that means you need to do interrupt on edge (plus & minus) of both chann=
els.
>> I would guess that is the mode you are in.
>> That give you the most steps per revolution.
>> X2 is easier and X1 more so if you do not mind less steps per revolution=
s.
>>
>> 3x means you are not keeping up with changes.
>>
>> I could draw you a logic drawing for X1/X2/X4 that you can convert to lo=
gic.
>> Or a truth table.
>> Let me know.
>
> Hi Ray,
>
> I think I sort of understand what you're getting at. I'm not 100% sure
> how it applies to me though. My data sheet shows that at each detent
> my B channel should be transitioning. I'm not sure interrupt on change
> is a possibility in my situation.
>
> So...I guess what I'm saying is that I'm confused. Help!
>
> By the way, my current thought is to try feeding the port with my
> encoders on it through my debounce routine to see what happens if I
> verify all the current states. My only concern is that this might not
> be fast enough to capture a quickly moving knob (which isn't that
> quick, these are user controls, not on a motor). I'd still like to
> know for sure why this is happening though.
>
> Thanks!
>
> Josh
> --
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> completely foolproof is to underestimate the ingenuity of complete
> fools.
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