On Wed, 26 Jun 2002 15:11:08 -0400 Erik Jacobs <emj14@COLUMBIA.EDU>
writes:
> > to position. When in one of its stable positions, both sets of
> contacts
> > are open, so you can connect multiple encoders in parallel and
> adjust any
> > one of them and have the PIC read it fine. I managed to do it with
> > polling instead of interrupts. On detecting that the first contact
> had
>
> Well, what method did you use to "detect" that the "first" contact
> was
> closed?
>
> I'm thinking that if I AND the two outputs from the encoder, that
> could give
> an interrupt.  Then if you just polled until the state changed,
> you'd see
> which came up next (either 01 or 10) and that would tell you what
> direction
> you're going... yeah?

        I'm detecting the first closure using polling, then staying in a tight
loop (with a counter limit so I don't get stuck there forever) waiting
for the first closure to open. I then check the second set of contacts.
Their state tells me which direction the encoder is going.
        With interrupts, assuming the contacts are set up for a closure to
ground, you can just generate a negative interrupt on detecting the first
contacts closing, then check to see if the second contacts are open or
closed, which will tell you the direction of rotation. Interrupt response
time has to be fast enough to get there in time, but this should not be a
problem. In the project I'm using the encoder on, I've written the whole
thing in C and have not yet used interrupts. We'll see if I need to bring
them in a little later.

Harold



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