user4664: If you use an external oscillator, and divide-by-8 internally, can you apply up to 160MHz on PB6? For example, can I use my 50MHz oscillator to clock my 328p @ 6250KHz? Note: when I say oscillator I don't mean resonator or crystal

user13432: No! 20 MHz max (Please see 8.8 External Clock, pp. 34). The 50MHz clock could be divided by 8 with a counter or the 150MHz clock by 16 with a faster counter. 
Cheers!

4664: <p>If you use an external oscillator, and divide-by-8 internally, can you apply up to 160MHz on PB6? For example, can I use my 50MHz oscillator to clock my 328p @ 6250KHz? Note: when I say oscillator I don't mean resonator or crystal</p>
 13432: <p>No! 20 MHz max (Please see <a href="http://www.atmel.com/images/doc8161.pdf" rel="nofollow">8.8 External Clock, pp. 34</a>). The 50MHz clock could be divided by 8 with a <a href="http://www.nxp.com/documents/data_sheet/74HC_HCT393.pdf" rel="nofollow">counter</a> or the 150MHz clock by 16 with a <a href="https://www.fairchildsemi.com/datasheets/74/74VHC393.pdf" rel="nofollow">faster counter</a>. </p>

<p>Cheers!</p>
