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!