Hi Bigfun,
Good stuff ! CosineKitty's discovery could be really useful. I wonder if it could be used to transmit data...
1,000,000 iterations / 644 milliseconds = 1,552 iterations per milliseconds.
Given that you need two iterations to make a square wave (first to set to 1, second to set back to 0, ^= is an XOR don't forget), the frequency is 776.397kHz, isn't it ?
Lionel.