What kind of IC is this

Dave McGuire mcguire at neurotica.com
Wed Dec 31 09:57:11 CST 2008


On Dec 31, 2008, at 9:27 AM, Jules Richardson wrote:
>> Ok, i don't know much CPUs with onboard ROMs, but I think it  
>> should work
>> with Zilogs Z8 with on-chip ROM - or am I wrong at all?
>
> That reminds me - I keep meaning to look up details on the Z8. I  
> was told once that it was just a Z80 with on-board ROM, but that  
> never explained why I had one in the junk box marked "Z8 ROMless"...

   "The Z8 is an embedded version of the Z80" is a very common  
mistake, one I've even seen in print in magazines.  Nothing could be  
further from the truth...it is a completely different architecture  
that doesn't even bear a passing resemblance to the Z80.

   It's a pretty neat register-file-based architecture, kinda fun to  
program.  They've been around for a long while, and are still current  
products.  The current Z8 implementations are available in low-pin- 
count packages and are pretty fast.  What's lacking is free  
development tool support, which is sad, and very unusual for today's  
embedded world.

   Zilog did a nice BASIC, which they shipped in a mask-ROM version  
(Z8671) which Steve Ciarcia had a ball with in several of his BYTE  
Magazine articles.  There's also a Forth implementation which I've  
messed with, after having typed in the entirety of a faded printout  
of a hex dump in order to get into digital form...that was tedious.

   Your "Z8 ROMLESS" chip is just that; a Z8 microcontroller that is  
designed for use with an external ROM.  Still others (Z8603, Z8613)  
are available which have a 24-pin EPROM socket permanently mounted  
atop the ceramic 40-pin DIP, with the die well pushed off to one side  
to make room for it.  It's neat.  I've got quite a few of those;  
they're what I use to mess about with the Z8671-shipped BASIC, and  
the Forth system I mentioned above.

   Here's a pic of a quickie board I threw together to exercise both  
the BASIC and Forth implementations, using one of those "EPROM socket  
on top" chips:

   http://www.neurotica.com/misc/Z8-board.jpg

              -Dave

-- 
Dave McGuire
Port Charlotte, FL





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