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

Thanks Peter, I had a feeling I was stepping into no-man's-land. I forgot about the effects of oscillator discontinuities on the operation of the SX. Ive looked a bit for a programmable oscillator capable of both 100kHz and 50MHz but didn't find one in my brief search. 


William, it has struck me that you may be approaching this issue from a hardware perspective when it can be more easily accomplished via software. Depending on the nature of the power up for the SX in its high speed mode, you can combine the SX's power-down mode with either MIWU or RTCC interrupts. The RTCC will wakeup the SX periodically so that it can do a few computations and optionally go back to sleep, the MIWU will wake up the SX when a pin change on a port B pin occurs at which point the SX can either go back to sleep or stay in its high powered mode. (The WDT interrupt can also work if you need the RTCC for another purpose, but you don't have as much control on the time period between wakeups). Using one of these methods will dramatically reduce the power consumption of the SX since the SX only consumes microamps during power down (<300uA w/o WDT, <400uA w/ WDT). 

One final complication to the hardware approach, the Oscillator setting for the SX would need to be HS1,HS2 or HS3, but this isn't the best choice for a 100kHz clock (likely the XT1 option) but this option is set via a fuse at program time and is not settable at run time.

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