IIc+ overclocking

[Jorge Chamorro Bieling]

Hello,

I think I read somewhere about overclocking the IIc+.

Is the oscillator the only thing I have to replace or do I have to
replace the cpu and/or the memory chips also ?

Are there any (bad) side effects ?

Anyone that has done this and can tell me about it?

Thanks,
--
Jorge Chamorro Bieling

[julian814]

Hey, Jorge.

I remember seeing that thread not too long ago in this newsgroup, but I
can't remember the name of it. Somebody on eBay was selling and
overclocked //c+, and showed the modifications in his auction. You
might want to try using Google groups to find it.

Ralph Glatt

[Michael J. Mahon]

Jorge Chamorro Bieling wrote:
> Hello,
>
> I think I read somewhere about overclocking the IIc+.
>
> Is the oscillator the only thing I have to replace or do I have to
> replace the cpu and/or the memory chips also ?
>
> Are there any (bad) side effects ?
>
> Anyone that has done this and can tell me about it?

I haven't done it myself, but several here have.

It only involves replacing the crystal oscillator. There
are no downsides, apart from faster game action. ;-)

Unlike modern overclocking, where thermal effects are significant
and potentially damaging, overclocking a IIc+ is benign. And it
is the only Apple II model that can be easily overclocked, because
it already isolates the rest of the system from the processor clock.

-michael

Music synthesis for 8-bit Apple II's!
Home page: http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."

[Jorge Chamorro Bieling]

Michael J. Mahon <mjm...@aol.com> wrote:

> It only involves replacing the crystal oscillator. There
> are no downsides, apart from faster game action. ;-)
>
> Unlike modern overclocking, where thermal effects are significant
> and potentially damaging, overclocking a IIc+ is benign. And it
> is the only Apple II model that can be easily overclocked, because
> it already isolates the rest of the system from the processor clock.

Do you think that it will go up to 12MHz with a 16*3 MHz oscillator ?
Or even more if I replace the cpu/memory ?
Or it's better to stay at 8 MHz ?

Thanks.
--
Jorge Chamorro Bieling

[Mark Frischknecht]

If you are gonna just over clock and not change the cache size all you
need to do is replace the Osc. But to be safe I replaced the SRAM with
faster versions.

Hear are a few images of what I did:
http://www.appleiiguy.net/images/iicplusmod01.JPG
http://www.appleiiguy.net/images/iicplus02.jpg
http://www.appleiiguy.net/images/iicplus03.jpg

And a link to the Thread discussing it.
http://www.applefritter.com/node/9898

Mark Frischknecht

[Mark Frischknecht]

Unless you replace the CPU you will be stuck at 8 mhz.

Mark Frischknecht

[PZ]

Without ever looking into a Laser 128ex, I wonder how easy it would be
to tweak one of them? We would benefit from having a slot.

- Paul

[Jorge Chamorro Bieling]

PZ <skie...@yahoo.com> wrote:

> Without ever looking into a Laser 128ex, I wonder how easy it would be
> to tweak one of them? We would benefit from having a slot.

Is it a special slot or a normal a2 slot ?
--
Jorge Chamorro Bieling

[Jorge Chamorro Bieling]

Mark Frischknecht <apple...@gmail.com> wrote:

> If you are gonna just over clock and not change the cache size all you
> need to do is replace the Osc. But to be safe I replaced the SRAM with
> faster versions.

Hmm... you say change the cache size ?
I'm not sure that you can do this easily ?

If the address line a13 is connected to the memory socket, it would have
to be at pin 26 and that is cs2 in the 6264 (a 16k 62128 would need it
there). If you go with a 62256, then a14 goes to pin 1 that is a no
connection in the 6264 (and this is good).

But, if these signals were being feeded right now to the memory socket,
(and we forget that a13 is a chip select in the 6264) then I think the
cache "subsystem" would be badly misbehaving as it would be "rolling
over" every 8kb which is not good..

Please take a look at the pdfs of these memories, I have "saved" them
here:
<http://homepage.mac.com/jorgechamorro/a2things/>

And tell me if you think I'm right.

I see your new memories are 100ns parts. What was the speed of the
memories that you pulled ?

I'd like to speed the cpu to 14MHz, but I dont think that the asic that
controls this cache stuff will support it, that's almost a x4 overclock!

BYW, you should have put a socket to the oscillator...

Thanks Mark,
--
Jorge Chamorro Bieling

[PZ]

AFAIK, its a normal A2 slot.

- Paul

[Mark Frischknecht]

I Did put a socket in. And my SRAM is now 70 ns. The Sram chips are
HY6264LP-70 (8k by 8 bit CMOS SRAM's)

[bie...@terra.es]

Mark,

You say nothing about the cache size.
What do you think about it ?
Have you tried with other clocks/speeds in your IIc+ ?

Thanks, Jorge.

[Mark Frischknecht]

To use a different cache size you need to add more wires and I dont feel
comfortable doing that. I tried a 66.66 Mhz osc (16.66 Mhz //c+ speed)
and a 50.00 mhz osc (12.5 Mhz //c+ Speed)and It didn't work (Like I
expected) because I am still using the stock processor. But it is
running fine at 8 Mhz. I plan on purchasing a new 14 MHZ rated processor
from WDC. I expect it to run fine at 12.5 mhz with a new processor.

Mark Frischknecht

[aiia...@gmail.com]

> I expect it to run fine at 12.5 mhz with a new processor.

That will be a speedy apple II.

Rich

[PZ]

Your cache will crap out 1st. You need to get faster SRAMS than 70ns.
Digi-key has 600mil to 300mil socket adapters, you'll want to install
those first since you won't find much faster SRAMS in 600mil. Next
pick up some 15-20ns SRAMS (preferably Japaneese). Make sure
everything works at stock speed before you try the fast XTALs.

- Paul