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In article <1992Aug27.135703.26001@zip.eecs.umich.edu> johnwitt@cdrom.engin.umich.edu (John P Wittkoski ) writes:



>For a 33MHz 68030, there is a minimum clock speed listed for it in
>the databooks. I think it's somewhere around 25Mhz for a 33MHz version, but I
>don't have my databook handy.

>My question is: why is there a minimum?
>One possibility I have heard is that the on-chip registers and/or cache
>are dynamic in nature, and since the chip is geared for 33MHz, it divides
>this down to whatever rate is needed for the refresh circuitry. Therefore,
>if you go below the minimum, the refresh rate slows to below the minimum
>needed for the refresh.

>Now, is there someone out there who knows about this? I'm interested
>specifically in the 68xxx CPUs, but any general info would be helpful.
>For example:
>1. Is the guess I made above accurate, or is there some other reason?
>2. If the reason above is correct, does it apply to the registers, the
>   cache, or both (or neither?)
>3. If it's just a testing parameter, how far could I crank the clock speed
>   down? 20Mhz? 16,8,2,1???

>Just curious.
>Reply by newsgroup or email, whichever is easiest for you.

>        --John Wittkoski
>          University of Michigan
>          johnwitt@engin.umich.edu



Yes, all registers (memory locations) on the processor are dynamic, and they 
get refreshed by cycle stealing mode (transparent to the system).

1- Your guess is correct.
2- It apply to all memory locations. Notice that static RAMs consume a lot 
   of real estate.
3- It is not testing parameter, but you can change the frequency down until 
   the system crashes; That is the minimum.



Peace and Prosperity!
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