Date   : Fri, 10 Jul 1992 19:01:18 GMT
From   : cis.ohio-state.edu!zaphod.mps.ohio-state.edu!wupost!sdd.hp.com!uakari.primate.wisc.edu!usenet.coe.montana.edu!news.u.washington.edu!sumax!ole!rwing!fnx!del@ucbvax.Berkeley.EDU (Dag Erik Lindberg)
Subject: Re: undocumented Z80 Ops

u8515682@cc.uow.edu.au (Wayne Jefferson Doust) writes:

>Why did Zilog produce a chip with codes that were not documented?
>I don't understand.

I don't think it was really their intent.  They produced a chip that did
the things they wanted it to do.  The 'undocumented' codes are actually
just by-products of the way the internal decoding is done by the CPU.
Actually, 'unsupported' would be a more accurate term.  Zilog recognized
that some usefull things could be done with those op-codes, but flat
stated that if their manufacturing process changed, or micro-code was
modified, those op-codes may not work any more.  As it turned out, the
Z80 sort of dead-ended development wise, and that never happened.

-- 
del AKA Erik Lindberg                             uunet!pilchuck!fnx!del
                          Who is John Galt?