Apple //c++ experiments...

["Michael J. Mahon" <mjmahon@aol.com>]

I recently acquired a //c+ (Yay!), so I decided to try replacing the
16MHz accelerator oscilator with a 32MHz oscillator to bump the speed
from 4MHz to 8MHz (making it a "//c++"  ;-).

I was concerned that simply replacing the oscillator might shorten
the "slowdown" times for slow slots and the speaker and joystick,
which could pose a problem.

The answer is that the slowdown times are timed by counting down
the 1MHz Apple bus clock, not the accelerator clock, so they are
unaffected by oscillator frequency--a very convenient result.

Also, the Zip Chip Utilities, and in particular the ZIP.SYSTEM program
that runs before any other system program on the boot volume, configures
the IIc+ just as it would for any slotted Apple II.  Of course, it is
necessary to leave slots 5 and 6 slow for disk access to work, and in
the IIc+ it does not appear to be possible to set the joystick to
"fast" (but the speaker can be set to fast).

In short, just replacing the 16MHz oscillator with a 32MHz oscillator
converts a IIc+ into a "IIc++", and the Zip utilities can be used to
configure the actual speed, or even to default the accelerator to "off".

BTW, I understand that some IIc+ machines will not run with a 32MHz
oscillator.  I have several 32MHz oscillators, and found that one type
would not work, while another (RXD 1100) did, so maybe the problem
some have reported is an oscillator problem, not a IIc+ problem...

I tried a 39.750MHz oscillator, and it didn't work--but it was of the
same type that did not work at 32MHz, so I don't think that proves
anything.  I was hoping it would work, so that I could run at 32MHz
with some assurance of some "headroom" for reliability...

-michael

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