Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!seismo!rutgers!ucla-cs!cit-vax!ll-xn!ames!ucbcad!ucbvax!decvax!ima!johnl
From: johnl@ima.ISC.COM (John R. Levine)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Strange 8086 CPU clones.
Message-ID: <618@ima.ISC.COM>
Date: Wed, 15-Jul-87 23:46:38 EDT
Article-I.D.: ima.618
Posted: Wed Jul 15 23:46:38 1987
Date-Received: Sat, 18-Jul-87 04:26:12 EDT
References: <3995@vrdxhq.UUCP> <1610016@hpcvlo.HP.COM> <4022@vrdxhq.UUCP> <1609@leadsv.UUCP>
Reply-To: johnl@ima.UUCP (John R. Levine)
Organization: Javelin Software Corporation
Lines: 14
Summary: undefined opcodes do whatever they happen to do

In article <1609@leadsv.UUCP> hooper@leadsv.UUCP (Ken Hooper) writes:
>WHAT DOES THE *@^&%%#% 8086 DO WITH A BAD OPCODE?

Well, it, uh, excecutes it.  You get whatever you get when you run those
bits through the instruction decode logic.  By and large, they're no-ops,
but the 8086 does seem to have some strange instructions like POP CS which
may have been built in deliberately or may just have happened.

This is in the fine tradition of the PDP-8 in which every possible bit
combination did something or other.
-- 
John R. Levine, Javelin Software Corp., Cambridge MA +1 617 494 1400
{ ihnp4 | decvax | cbosgd | harvard | yale }!ima!johnl, Levine@YALE.something
U.S. out of New Mexico!