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Re: Apple IIc+ @8Mhz
Hotte wrote:
The new design will
not require the case to be altered from original.
I like to hear that, I do all my tinkering on the Apple the same
way... the "stealth mode".
As I am fine with switching between 1Mhz and full throttle , I have
not bothered to think about some softswitching.
But my original posting was about going beyond 8-10 Mhz .
Is it possible with faster CPU and RAM?
Or is there other stuff which than limiting the speed?
There certainly is other stuff limiting the speed!
The ASIC is in the middle of all the datapaths, and you
pretty much have to live with it, since faster replacements
are not available.
All integrated circuits have a "speed range" which is only
guaranteed to *include* its actual speed rating. Given the
quantities in which Apple procured parts, it is likely that
many chips were actually capable of higher than their rated
speeds. This will not be evident until an experiment is
performed.
Any of the ICs can be the limiter, so the appropriate way to
maximize speed is to replace everything replaceable with either
faster or different components to see how the maximum reliable
operating speed is affected. This would actually be best done
with a variable frequency oscillator, so the actual failure
point could be determined for each substitution.
After speed is maximized for one component, other components
that were not previously limiting the speed may be found, and
so on, cyclicly.
As an added complication, depending on the logic design of the
circuit--especially the ASIC--it is possible that substituting
a *too fast* component could cause a failure (though that is
unusual) because of marginal timing at the interface to another
component. In general, a digital input to a circuit must take
its final value for some time before it is sampled by the next
clock (setup time) and hold its value stably for some time
after the clock (hold time). If both constraints are not met,
the circuit may produce incorrect results.
In any case, an accelerated machine (even a stock IIc+) can
be slowed down to any of a variety of speeds by running the
Zip Utility program, which is often installed on a boot disk
so that it runs just after ProDOS loads and before the usual
.SYSTEM program.
-michael
NadaNet file server for Apple II computers!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."