dlloyd:
I'm not familiar with your analyzer, but I'm referring to the trigger voltage (reference signal), not time base or sample frequency. Your logic analyzer will internally have a comparator and it will be creating an output signal based on if the input signal is > or < a reference signal.If this reference voltage is near any noise level or logic level at the input, then a false output would occur. Make sure your input isn't loaded by other probes or devices and that there's good grounding.
Thanks, good advice, but I have looked at all of this and measurement are consistent even with triggering off. You will note that the code runs "forever" so it does not really matter where you start --
Except for the phase, and except that when using micros there is supposed to be a roll over about ever 70 minutes.