Path: utzoo!attcan!uunet!telesoft!roger
From: roger@telesoft.UUCP (Roger Arnold @prodigal)
Newsgroups: comp.arch
Subject: Re: 8086 design goals (and Pascal)
Summary: ancient history question
Message-ID: <370@telesoft.UUCP>
Date: 17 May 89 22:53:29 GMT
References: <912@aber-cs.UUCP> <3312@bd.sei.cmu.edu> <362@verdix.verdix.com> <15766@vail.ICO.ISC.COM>
Organization: TeleSoft Inc., San Diego, CA
Lines: 27

Since this news thread is dealing with ancient Intel history, I'd like
to ask a question I've long been curious about, and have never seen a
definitive answer.  Maybe enough time has gone by to get a straight 
answer from someone involved with the project and no longer working 
for Intel...

What I'd like to know is what was the story behind the undocumented
instructions in the 8085?  And, as a bonus question, do the chips
currently being produced still include those instructions?

The 8085 was really a much better chip than Intel advertised.  The
undocumented instructions extended the 8080 instruction set in what I
considered to be a cleaner and more natural manner than the glitzier
extensions in the Z80.  As a compiler writer, I would have found them
very useful.  I did use them in assembly code on my old IMSAI machine.
But Intel chose to pretend that they weren't there, and marketed the
8085 strictly as an upgraded 8080, with an easier system interface and
more efficient bus.  

I suppose they didn't want to invite comparison between the 8085 
extensions, and those of the Z80 that were out first.  And/or they
didn't want to steal any fire from the upcoming 8086.  But it always
struck me as wierd to have those nice extensions fully implemented
in the silicon and usable by anyone who knew about them, but never
even acknowledged by the chip's maker.  

- Roger Arnold				..ucsd!telesoft!roger