Path: utzoo!utgpu!watserv1!watmath!att!att!linac!pacific.mps.ohio-state.edu!zaphod.mps.ohio-state.edu!wuarchive!cs.utexas.edu!sun-barr!apple!apple.com!Alkire From: Alkire@apple.com (Bob Alkire) Newsgroups: comp.arch Subject: Re: The CPU with 3 brains---486 compatibility with 8008 Message-ID: <11297@goofy.Apple.COM> Date: 17 Nov 90 00:27:17 GMT Sender: usenet@Apple.COM Organization: Apple Computer, Inc. Lines: 31 References:<42737@mips.mips.COM> <1990Nov4.014901.23819@zoo.toronto.edu> <1990Nov6.223738.13265@ux1.cso.uiuc.edu> <9333@b11.ingr.com> >lhughes@b11.ingr.com (Lawrence Hughes) writes: >>The Z80 WAS upward compatible with the 8080, at both architecture and binary >>opcode level... > em@dce.ie (Eamonn McManus) replies: >This isn't *quite* true. The parity flag on the 8080 became the >parity/overflow flag on the Z80. This meant that arithmetic instructions >which affect this flag as parity on the 8080 affect it as overflow on the >Z80. >I would not be surprised to discover that there are no programs in existence >that are affected by this change ... Most CP/M-based programs that were written for the 8080 did run without difficulty on the Z80 with one well known exception: Microsoft Basic. There was a three instruction patch to fix it that I believe was written up in a very early issue of Dr. Dobbs. Bill Gates was using a jump on parity after a arithmetic instruction for some yet to be understood reason. Bob _k Monday $ 30,510,000 $ 41,135,000 Tuesday $ 39,233,000 $ 37,242,000 Wednesday $ 43,708,000 $ 37,715,000 Thursday $ 37,056,000 $ 44,668,000 Friday $ 39,941,000 $ 34,074,000 Total $190,448,000 $194,834,000