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Re: Speed check



Sheldon Simms wrote:


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


I think you'll find that that SRAM is 100ns, not 10ns but I don't think
that that's the bottleneck. I tried some 35ns SRAM but it didn't help
any.

The IIc+ I had apart last night uses the same processor as yours. My
other one came with a different brand of processor, a Rockwell R65C02P4.
I have a few of these but unforunately I can't boot at the same speed
with these as with the other processor.
My first suspicion is that the processors too slow. Unfortunately
getting a faster 65C02 without having to order $100 worth of 65c02s
might be a problem.
Still 8 or 10mhz on a IIc+ isn't bad.

Wayne