Re: Speed check

[Sheldon Simms <sheldonsimms@yahoo.com>]

On Wed, 20 Aug 2003 07:23:17 +0000, Michael J. Mahon wrote:

> Wayne Stewart wrote:
> 
>>I pulled the 16 mhz oscillator out of my IIc+ and installed a socket
>>and tried some oscillators. I was able to boot up with a 40 mhz
>>oscillator but not a 42 mhz. So far no problems with either the
>>built-in drive or an external 5.25" drive.
>>
>>Does anyone have any utility that might clock a IIc+?
>>
>>I'll see about trying some faster SRAM and maybe a faster processor
>>if I have one
> 
> Far out!!  I been wondering how far overclocking could take a IIc+!
> 
> A simple speed test is to write an Applesoft program to do a
> FOR-NEXT delay loop, then beep, then loop back to the delay.
> The rate of beeping is easily timed and gives a useful speed
> ratio.  (The beep will probably run at normal speed, but the
> majority of the time is spent in the FOR-NEXT, which should
> run at full speed.)

As soon as I read the original post, I whipped out my soldering
iron and went to work. I socketed the oscillator and then started
trying out different speeds. For me, the fastest working oscillator
is 32 Mhz. At 40 Mhz it almost works, but crashes into the monitor
at startup.

I don't think the SRAM is a problem here, at least on my IIc+.
Mine has 12ns SRAMs built in and that should be good enough for
a 64 Mhz oscillator at least. However, I do notice that the IIc+
has a 74F00, just like the Zip GS board, so I'll try replacing
that with a 74HC00 first and see what that does.

After that I might look at the cpu. My IIc+ seems to have a 65c02
that was custom made for Apple. The markings are:

  VLSI
  8843AV  R0804
  VC2995-0001
  344-6502-1
  (R)(C) APPLE '87

I'm guessing that Apple licensed the core from WDC and had VLSI
manufacture the chips. I don't have any idea what it's speed rating
would be...

-Sheldon