I need to have the lowest power possible while logging data for up to a year on a small 3.6 volt lithium battery but I also want a fast download to dump the very large data file of 128 MBytes after the data logger has been retrieved many months after deployment. Can I have a PIC running on a 100 KHz crystal while in data gathering mode and just force an external 20 MHz clock into CLKI/OSC1 for the data dump phase. I want to leave the 100 KHz crystal in place between OSC1 and OSC2 and just force a 1 volt peak to peak 20 MHz signal in for the data unload phase.

Has anyone tried this dual clock speed approach before? Any problems I should look out for?

BrianT