Internal RC Oscillator Calibration

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While I was working to get usart debug statements into my frequency detection application (which STILL doesn't work), I got to wondering how the values in OSCCAL get set. Yes, I have read the datasheet and I understand that OSCCAL is populated at power up. What I am curious as to how does Atmel test and program the values in the first place? Do they test each chip or sample the wafer? Once they have the values, is there some secret incantation that allows them to program the values or are there 'pins' on the chip that are covered up when the package is applied?

You can have my mac when you pry my cold dead fingers off of it.

Kevin McEnhill -- mcenhillk@gmail.com

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Those are good questions, Kevin. There was a thread about this a few months ago, but it did not answer all of your questions. IIRC, the OSCCAL is generated before packaging and that is what accounts for its relative inaccuracy. Pragmatically, what is important is that the accuracy of the programmed OSCCAL is stated in the datasheet (10% for the Tinyx5's at room temperature) and also Atmel provides a document and code to calibrate your AVR (AVR053 note) so that you have have stability as stated in the datasheet (1-2% for the Tinyx5's at room temperature).