>    I got the idea... I think that I can get as fast as
> a 10 mS or even a little less cycle time for a PI
> controller, but i am now tempted to use the on/off
> control...

You should be able to do better than that for a simple PI controller.

One of my projects runs two layered PID controllers in a 16F876.  The
lower one adjusts the PWM output to a DC motor to control its position,
and the upper one adjusts the motor position, which is connected to a
throttle of a gasoline engine, to control the engine's speed based on some
input parameters.  Both are full PID with a few other features added, and
both use software 24 bit floating point.  A new computation is done every
10mS, although the worst case computation time is about 7mS.


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