Newsgroups: comp.robotics
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From: tgb@bnu003 (Tom G. Brusehaver/Consultant Euler Solutions)
Subject: Re: Best microprocessor
In-Reply-To: huang@erie.ge.com's message of Tue, 21 Feb 1995 22:43:09 GMT
Message-ID: <TGB.95Feb27081044@bnu003>
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References: <3id31v$abl@acorn.acorn.co.uk> <D4DGFx.Ist@erie.ge.com>
Date: Mon, 27 Feb 1995 14:10:44 GMT
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 S> I think the Z-80 is opcode-compatible with the i8085.  It's more
 S> correctly described as a derivative of the i8085 rather than the
 S> i8080.
 
Nope,

Intel had the designers of the Z80 in their employ for the building of
the 8080.  Then the designer left to start Zilog, and the Z80 came
out.  

Intel then designed the 8085, not sure if it was to compete with the
Z80 or if the design was simplified before the Z80 was built.  

A functioning computer took 4 chips (minimum) for the 8080 (CPU, CLK,
??? and ROM).  Two chips each for the Z80 and 8085 (CPU ROM).

The 8080 code will run 100% on an Z80, but not the otherway around,
nor will 8085 code run 100% on the Z80.  Three(?) interrupt
instructions were added to the 8085 instruction set.

The Z80 had many documented instruction additions to the 8080
instruction set, and a duplicate set of registers.  There were also
many undocumented instructions in the Z80 (don't ask me what they
were, I have long since forgoten.  There was one that turned the chip
into an oven, cause it would loop in a part of the CPU causing some(?)
parts of the die to get really hot).

Tommy

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