In SX Microcontrollers, SX/B Compiler and SX-Key Tool, bean wrote:

At 500 RPM you are going to get a value of 12,000. 
12000 * 10 = 120,000 which is STILL greater than 65535.

Without doing anything fancy the best you could do is:

Do
  PULSIN RA.0, 1, Pwidth1
  PULSIN RA.0, 0, Pwidth0
  Temp = Pwidth1 + Pwidth0 
  Temp = Temp  / 100
  RPM = 60000 / Temp
Loop

This will give you 5Hz resolution at 500 RPM, but only 1000 hz resolution at 7000 RPM.

Bean.

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