>Dear All,
>        I'm writing the stepper motor control part of my PIC application
>which controls a telescope. The position is maintained by encoders which

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Have you given any thought to using digital setting circles for your
telescope controller.  These are very accurate and are readily available
for about $100 to $150.  They have MANY different functions and modes of
operation (both equatorial and alt/azm).  The model on my scope can be
set to display the distance that each axis is from a given object.  Once
both readouts are brought to 0, the desired object is in the field of
view.  You would need to get the information out of the setting circle
unit and into your PIC.  Maybe you could hack into the display and
capture it from there.  This information could then be used to control
your positioning motors.  Essentially, the digital setting circles would
function as your position encoders, but they would provide a good deal
more than that  i.e. built-in databases of objects, next closest object
to current position, etc. etc.

Just a thought.  Might not even be possible.