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

Rodney,

Now that I've been playing and digging deeper, I think your pitch table is off.  The reason is that you calculate the number of cycles for the entire period (P = 1/F, cycles = P/ISR_timing) but that's for the whole period; the ISR toggles the tone output when the cycles count is reached -- this means you have to divide the cycles count by 2 for each half of the square wave.  I verified this by calculating the half-cycles count for A4 (A4), let it play, and hooked up a 'scope.  The frequency was dead-on 440.  You can fix your program by dividing PitchCount by 2 before enabling the sound output in the ISR.  

I'm presently calculating a new table.

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