Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!tcdcs!dce.ie!em From: em@dce.ie (Eamonn McManus) Newsgroups: comp.arch Subject: Re: The CPU with 3 brains---486 compatibility with 8008 Message-ID: Date: 15 Nov 90 18:29:27 GMT References: <42737@mips.mips.COM> <1990Nov4.014901.23819@zoo.toronto.edu> <1990Nov6.223738.13265@ux1.cso.uiuc.edu> <9333@b11.ingr.com> Organization: Datacode Communications Ltd, Dublin, Ireland Lines: 17 lhughes@b11.ingr.com (Lawrence Hughes) writes: >The Z80 WAS upward compatible with the 8080, at both architecture and binary >opcode level... 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 (unless they use it deliberately to see which processor they are running on). About the only arithmetic instruction where you would be interested in the resulting parity is (in Z80-speak) `adc a,a' which rotates left the accumulator and carry. -- Eamonn McManus