>Q: Given N and M with N > 0, N < M, M <= maxcount, what is the largest
>space between realizable duty cycles?

The smallest step (delta) is 1/N where N is the maximum divider. There is
no way around this, unless. The o/p of a PWM waveform is integrated
directly. The value of the integral is written V = V1*M/N where V1 is the
amplitude of the PWM voltage and M<=N. There is NO way to reduce the step
below Nmin/M which is 1/M.

What you *can* do is use the tristate facility of the output pins. This
effectively increases the number of output encoding states. With this you
can have three output states so the output could be manipulated more
accurately OR faster with the same number of IO operations.

For example if you have to output a value N then decide if N is above M/2
(where M is the maximum output), or below, set output bit=((N - M/2) >=
0)?1:0; and output unipolar pulses using the tristate control only (i.e.
set bit value and turn on/off using tristate control). You can have 9 bits
resolution on an output with timing as for 8 bits (N = 256), or 8 bits
with timing for 7. Of course this assumes that the external hardware
cooperates and the output tends 'to' 1/2Vcc when the pin is not driven.
There are some more problems with this, so I have simplified here.

Peter

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