In SX Microcontrollers, SX/B Compiler and SX-Key Tool, Peter Van der Zee wrote:

Hi Tracy;

When I was having my debug at 3 volt problems two days ago I spent a bunch of time on these issues, and, among other things, I did exactly what you are saying. I happen to have a scope that can go to 500MHz, and a special 1.5 pF low capacitance probe good to 1 GHz to go with that, so I'm pretty sure my measurements were real.

The debugger defaults the oscillator setting to OSCHS1. In debug mode, you can only override that by changing the setting in the DEVICE panel, and then programming the chip via that avenue. The SXKey delivers an amplitude to the oscillator input pin -OSC1- pretty consistent, regardless of frequency, but the output observed on the oscillator output pin -OSC2- varied dramatically with the oscillator gain settings, from next to nothing to hitting the rails.

Guenther advises that in debug that is of no consequence..... I suspect therefore that during debug the chip uses the input pin of the oscillator, whereas while not in debug it would of course use the output pin, or some buffer close to there. I still think my debug problems were related to the gain settings, but hey, I'm runnin' right now, and I'll dig deeper some other time.

In one of my 3 volt scenarios (SX48) the oscillator will not run with a 50 MHz resonator and a gain setting of OSCHS3. I need to back it off to HS2.

So my take on all this is along the lines as Terry stated; crank it up till it quits working, and then back it off one notch. That is if you can afford the extra current, and if you can't, then I would crank it down until it quits , and then up it by a notch. And if the span is wide, then park it near the middle. But do keep operating temperatures and different voltages in mind.

Cheers,

Peter (pjv)

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