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Jeff Martin has worked out a very nice object that will support up to 16
rotary encoders.  I have attached the file, and derived some of the
formulas from the document that allows you to calculate the number of
'clock cycles' and maximum RPM the encoder can operate.

Total Cycles = 144 + 50*(Number of Encoders-1)

RPM of Highest Resolution Encoder = XINFreq * PLLMultiplier / Total
Cycles / 2 / MaxEncPulsesPerRevolution * 60

Example 1: Using a 4 MHz crystal, 8x internal multiplier, 16 encoders
where the highest resolution encoders is 250 pulses per revolution:
           Max RPM = 4,000,000 * 8 / 894 / 2 / 250 * 60 = 4,295 RPM

Example 2: Using same example above, but with only 2 encoders of 250
pulses per revolution:
           Max RPM = 4,000,000 * 8 / 194 / 2 / 250 * 60 = 19,793 RPM

Example 3: Same as Example 1 above except a 5MHz crystal is used with a
PLL value of x16 :

           Max RPM = 5,000,000 * 16 / 894 / 2 / 250 * 60 = 10,738 RPM

Example 4: Same as Example 2 above except a 5MHz crystal is used with a
PLL value of x16 :
           Max RPM = 5,000,000 * 16 / 194 / 2 / 250 * 60 = 49,484 RPM
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Hope this helps :)

Vern

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