Re: mega128 at 18.432 MHz

At 11:10 AM 1/8/2004 +1300, Jason Kyle wrote:
>At 16:42 07/01/2004 -0500, Dave VanHorn wrote:
>
>
>>>Would be quite useful to know if 18.432MHz is safely achievable.
>>
>>If it were, the part would be rated for it.
>
>Sure, no harm in exploring the possibility though.  It's not like there 
>isn't any other CPU or micro in the world that hasn't been overclocked.

Other than it being a colossal waste of time, no.


>>>Of note is the datasheet USART baud rate table showing clock frequencies 
>>>upto 20MHz.
>>
>>That is a holdover, from years ago, when atmel intended to introduce a 20 
>>MHz version.
>
>And prior to that a 24MHz version.

I didn't see that in anything since '95.

>>What is it that you think you can't do at F<=16MHz?
>
>What is the engine capacity of your car?  You *could* drive to work with 
>an 800cc 3 cylinder normally aspirated engine under the hood, but I bet 6 
>jelly beans you don't!

Clocking a micro faster than you need to is wasting power, and creating EMI.


>IMO you can't know what others are building and what their speed 
>requirements are :)

Nope. I know what the chip ratings are, and I know that going beyond the 
speed rating is inviting problems.
I have enough problems.
I know that every time I've seen something that "had to be overclocked", I 
was able to recode it to fit comfortably within the ratings.
In one case, 4x under the ratings!

>Sure most micro designs are usually clocked faster than they need to be 
>but what's wrong with some headroom?

Buy fast chips, write faster code, clock only as fast as you need to.
http://www.dvanhorn.org/Micros/All/Overclocking.php