Re: A fast Z80 on an S100 BUS

On Apr 6, 2:15 pm, mona...@xxxxxxxxxxxx wrote:
On Apr 6, 4:36 am, Alli...@xxxxxxxxxxxxx wrote:



On Mon, 6 Apr 2009 00:57:57 -0700 (PDT), mona...@xxxxxxxxxxxx wrote:
On Apr 6, 12:41 am, mona...@xxxxxxxxxxxx wrote:
On Apr 5, 6:42 pm, je...@xxxxxxxxx (Jeff Jonas) wrote:

Allison:

To date the fastest Z80 I've been able to buy was the Z84C50 at 10mhz.
There is supposedly a 20mhz flavor but finding one may be a real
challenge.  But thats the limit for a plug compatble Z80.

Oy - my Adaptec 1542CF SCSI card is out of reach.
That was Z80 based, but was it 10, 12 or 20 MHz?

On the other hand the 10mhz part wants memory down under 90ns
to run no wait states

Has anyone re-used cache-on-stick for that?
Lotsa 80486-vintage motherboards used 20-25 nS static ram
for cache, in convenient .3" DIPs.

I have to admit the 10mhz on S100 I do have is a screamer and only
gets beat by the Z280 as thats both 12.5MHz and uses the 16bit
transfer mode to fast local ram (doesnt hurt that it's rev-J with
working 256byte cache and MMU).  With those speeds I've readed
the point where faster is only an experiment and serves no useful
software purpose.

YAY for running "vintage" parts THAT STILL WORK FINE!

Allison/Jeff, I see digikey has a Z84C0020 in a DIP package listed
(Its listed as 20MHz)
Jeff I noticed above you had a Z84C50 at 10HMHz. Not clear to me how
they are
numbering these things. But if it rally can do 20 MHz that sounds like
the way for me to go.
Since we are talking (most of the time) at less than 64K RAM I will
just put it on the S100 Z80Board.
Any suggestions for the simplest/fastest static RAM.- Hide quoted text -

- Show quoted text -

Just noticed that Digi-Key dont actully have any in stock!  I ordered
2 from Future Electronics as you suggested Jeff.
While a few weeks off, would either of you guys be open to direct e-
mail's so I could share design layout etc.

Yes.  

Allison- Hide quoted text -

- Show quoted text -

Actually on the disk stuff I have a 4Mg Quasi disk (RAM memory disk)
so I'm in good shape there. I was thinking along the lines of using
one 128Kx8 bits static RAM chip. I see Cypress chips (CY62128) at
70ns. Have you see single chips faster. I'm trying to keep board
wiring down. With 128K I can used CPM3 banked.
One thing I could really use help on is putting together a simple
circuit to page into RAM above 64K. Ithaca Audio had a CPU board that
does this nicely. It's a port the you address and it allows you to
have an 8K window above 64K overlapping with an 8K block below 64K.
The window is movable and can also point to below 64K as well so it is
transparent.  Unfortunately they have much other stuff on the board so
I cannot really figure out the circuit.  Do you guys have such a
circuit.

Check the comp.os.cpm thread "A question about memory bank switching "
from a few months ago, and look at Harston's design. It's clever in
that it uses the 16-bit I/O addressing of the Z80 to control the bank
selection hardware. He discussed it with me recently so he should be
familiar with it.

There have been many bank-switching designs, and many discussions of
them. Most of the S-100 manufacturers have documented their methods in
their manuals, which are in the usual places. 8K or 16K banks seem
common enough, the old IMSAI/Altair days had 4K banks but that's
mostly became out of favor. Re-read old threads on this to see who
weighed in with what ideas.

Herb Johnson
retrotechnology.com
.

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