OSCTUNE Tuning range

[MikeBZH]

Hi,

I plan to use a 18F2685 and my application requires some frequencies to be adjusted for a correct result. Using the internal oscillator and its capability to be adjusted via OSCTUNE seams to be a good solution but I cannot find anywhere in the datasheet a specification of the tuning range. I have read +/- 12 % of the nominal frequency. Is it correct ? Where does it come from ?

Thank you for your help

MikeBZH

[tenaja]

Some datasheets do not specify the range; you might have to look at the reference manuals to read that.

When I did not have online access and needed the answer, I just ran a loop, measured it on the scope, then adjusted and remeasured. Some adjust by .125% for each bit, I think they are not all the same, though.

[MikeBZH]

Hi tenaja,

That's finally what I did yesterday and I found roughly +/-12 % on this particular µC I was testing. But this does not give me any guarantee about the fact that all the 18F2685 parts have the same tuning range. As I am going to start a production this is important for me. I am going to look for a reference or maybe ask the question to Microchip.

Thank you for your help

MikeBZH

[languer]

Asking Microchip is the correct answer. I do believe what you found by testing is probably the answer though. Some datasheets do state +/- 12%, and AN244 states "OSCTUNE is responsible for tuning the frequency within a range of +/-12 percent on the selected frequency.".