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From: uhclem@trsvax
Newsgroups: net.micro
Subject: Re: Fast Z-80s?
Message-ID: <53400087@trsvax>
Date: Thu, 21-Nov-85 10:44:00 EST
Article-I.D.: trsvax.53400087
Posted: Thu Nov 21 10:44:00 1985
Date-Received: Thu, 28-Nov-85 03:17:50 EST
References: <10400207@uiucdcs>
Lines: 56
Nf-ID: #R:uiucdcs:10400207:trsvax:53400087:000:2398
Nf-From: trsvax!uhclem    Nov 21 09:44:00 1985


<What do you mean? How can the buss be in "For Future Use" Phase? Oh, its SCSI.>

According to the 1983/4 Components Data Book from Zilog, the fastest part
is the Z8400B at 6mhz (Z80B), which is available in Ceramic, CerDip and Plastic.
I have seen in the trade magazines (a year ago or so) ads for the Z80H,
which was a 8mhz part, but it is in none of the databooks I have.
Contact your local Zilog rep;  they will be able to tell you the status of 
this part.  (There is a Z80L, but I think it is a low power version.)
Mostek (does/used to/still might) second-source Z80s, so you might get a
good deal on one from them.


Also, the Hitachi HD64180 is a microcode version of the Z80 that runs at
up to 6mhz.  It has a higher mip-rate than a normal Z80 since most
instructions execute in fewer cycle-counts.  It also has two DMA channels
on board and a bunch of other cute things.
The chip does have a few drawbacks.  It only implements the documented
Z80 instructions.  All of those half-loads of the index registers are not
available.  If fact if you try an undocumented instruction, this chip
generates an illegal instruction trap, sets a flag and calls location 0.
On most existing Z80 systems, this reboots the machine.
Also, after reset it comes up with 3 wait states on all memory & I/O
references and lots of refresh cycles.  In existing boot code, this
usually means that the floppy driver will run too slowly and will not
be able to pull the data bytes in fast enough, resulting in lost data errors.
If you can add 22 bytes of OUTs to program the chip in the boot code,
then it works just fine.










It does have some nice new instructions like a Multiply and word I/O
instructions, and a lovely MMU on board fo 512K memory.
(This is the same chip used in the Byte board a few months ago.)
In a IM0 or IM1 environment, it works just fine.  I have not had much
luck getting it to replace a Z80 in a IM2 processor.  After a interrupt or
two the system croaks. 


<This information is provided by an individual and is not nor should be
 construed  as  being  provided  by  Radio  Shack or Tandy Corp.  Radio
 Shack/Tandy Corp has no obligation to support the information provided
 in  any way.  The Z80 is not IBM compatible.>
						
"The crime of copy-protecting bears bitter customers - The Lawyer knows!"(tm)

						"Thank you, Uh Clem."
						Frank Durda IV
						@ <trsvax!uhclem>