Z80 softcard- able to run at 7mhz/ faster than stock?

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Joined: May 2 2010
Posts: 47

Hi

I have a Iie enhanced and a iigs. Both machines have z80 cards. One genuine Ms, one a clone.

I read ages ago about running the z80's at a higher clock rate , and a recent search found this link :

http://www.appleii-box.de/appleboxAppleIIZ80Tuning.htm

Which I think is speedyg's site. No doc there at present.

Can someone advise please if such a mod is possible, is it worth it and how to do so? Each of my apples is otherwise stock, ntsc machines (being used in UK)

Tia, Iain

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speedyG's picture
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Joined: Nov 16 2011
Posts: 2376
Re: Z80 softcard- able to run at 7mhz/ faster than stock?

Hello iainjh,

Update after upgrade of the site....
new pagelink of the related page is:
http://www.appleii-box.de/C03_AppleIIZ80Tuning.htm

your correct - it´s my site and the mod was published in the early 80´s at the German
magazin. Thanks for giving me the hint that the pictures aren´t present anymore....
seems a unexpected dirmove caused the trouble.
this has now been corrected. At the end of the page is a link to a PDF-file
containing all the stuff of the page.

It was not a common modification because most Cards have been equipped with Z80A
and that chip only works safe up to 2 Mhz. Even Z80B chips are only safe up to
4 or 5 Mhz. But some of the Z80B chips from Zilog work fine at 8 Mhz.
So it´s a bit of gambling and swap and try to get from a bunch of Z80B chips
one being able to handle the speed....

Another point is also explained in the published doc:
the mod only works at the Apple IIe not in the II+ or earlier....
one of the reasons is the far slower RAM used in that old computers...
most II and II+ have only RAM withspeed of 300nS ( defined by the extension in the chipname 4116-3 )
and DMA won´t work with that slow RAM.
It seemed by experiments that the RAM chips must have at least a speed 150 nS or less.
This is only given at IIe and IIGS models.

Finally another point not mentioned....
the mod only works with CPM 2.20 or similar not with CPM 3.0 or above...
that versions of CPM demand a Z80 Card with at least 64 kB "on Board" at the card itself !

speedyG

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Joined: Jun 15 2014
Posts: 305
Re: Z80 softcard- able to run at 7mhz/ faster than stock?

Many II+ clones use one bank of 8* 4164-15 or faster...Not remembering now the Apple II peripheral bus organization I wonder how can the DMA be faster than the slots/bus design allows, e.g. 1/2MHz? I am also interested to see this softcard 7 MHz modification. SpeedyG, you said you have masters degree, so the the proper writing of Hz is with capital letter...

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Joined: May 2 2010
Posts: 47
Re: Z80 softcard- able to run at 7mhz/ faster than stock?

Awesome thank you!

I shall try and will report back. I have a few z80 machines that will lend a cpu for a test:)

More in a few weeks Smile

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Joined: Nov 16 2011
Posts: 2376
Re: Z80 softcard- able to run at 7mhz/ faster than stock?

georgel wrote:

Many II+ clones use one bank of 8* 4164-15 or faster...Not remembering now the Apple II peripheral bus organization I wonder how can the DMA be faster than the slots/bus design allows, e.g. 1/2MHz? I am also interested to see this softcard 7 MHz modification. SpeedyG, you said you have masters degree, so the the proper writing of Hz is with capital letter...

i assume you can at least read without support....
link is above....
no more answers to you....

__________________

In early days I had a lot of money but no time - now I have no money but a lot of time....
the second part includes less friends but a lot more joy on life....

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Joined: Jun 15 2014
Posts: 305
Re: Z80 softcard- able to run at 7mhz/ faster than stock?

Since Firefox opens the page without the article itself here is the direct link I found using Opera http://www.appleii-box.de/APPLE2/AppleIIeZ80Modifikation7MhzSpeedUp/AppleIIeZ80Karte7MhzSpeedUpModification.pdf
It is easy to find nowadays a factory rated faster Z80s like Z80H and use it without "gambling"...