External clock pro AVR

[Jan Waclawek]

Ivo Strasil wrote:
> L. Kavan wrote:
> 
>>>Ked uz ste spominali kalibraciu interneho oscilatoru u AVR, aku metodu
>>>pouzivate pri kalibracii?
>>
>>Byl to jen pokus jestli se da spolehnout na tovarni ladeni: 0x55 dokola ven
>>ze seriaku, mereni osciloskopem, kontrola prijmu na PC, ladeni oscilatoru
>>by-voko az se trefim ;-)
> 
> 
> Na malych rychlostech je celkem pekne mozne nastavit UBRR nebo OSCCAL
> podle mereni casu mezi hranami prijimanych dat. Da se zavesit i na jiny
> presny
> signal, ktery mam k dispozici, treba na frekvenci site.
> Zkusmo nastavit OSCCAL a doufat, ze mi to neujede, bych si asi nedovolil,
> pokud
> by neslo o vec vylozene pro mou potrebu.
> 

Je to mozno prekvapive, ale ATMEL ma niekolko appnotes na tuto temu.
http://www.atmel.com/dyn/products/app_notes.asp?family_id=607

AVR054: Run-time calibration of the internal RC oscillator   (19 pages, 
revision A, updated 09/04)
This application note describes how to calibrate the internal RC 
oscillator via the UART. The method used is based on the calibration 
method used in the Local Interconnect Network (LIN) protocol.

wek