Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!mimsy!cvl!umd5!zben
From: zben@umd5 (Ben Cranston)
Newsgroups: comp.sources.d
Subject: Re: Z80 -> 8080 converter
Message-ID: <1420@umd5>
Date: Fri, 16-Jan-87 01:28:13 EST
Article-I.D.: umd5.1420
Posted: Fri Jan 16 01:28:13 1987
Date-Received: Fri, 16-Jan-87 21:58:00 EST
References: <249@rocksanne.UUCP> <175@herman.UUCP> <707@argus.UUCP>
Reply-To: zben@umd5.umd.edu (Ben Cranston)
Organization: University of Maryland, College Park
Lines: 28
Keywords: Z80 8080 converter
Summary: Stop, you're both right

In article <707@argus.UUCP> ken@argus.UUCP (Kenneth Ng) writes:
> In article <175@herman.UUCP>, det@herman.UUCP (Derek Terveer) writes:
>> In article <249@rocksanne.UUCP>, stein@rocksanne.UUCP (Adam Stein) writes:
>>> ...Z80 to 8080 program converter.  ...
>> I believe that z80 has a mere two instructions that 8080 doesn't have.
>> Therefore, most likely, your z80 program will run unchanged with the 8080
>> assembler (I hope i'm right in this).  (As long as the z80 code doesn't use
>> those two instructions that is)
> The z80 has a LOT more than 2 more op codes over the 8080.

Ahem.  The 8080's instructions were completely specified by the first byte
of the opcode (the remaining bytes were addresses and such).  The Z80 used
two previously unused values of this first byte for the added instructions, 
but they both involved a SECOND byte to completely specify the additional
instruction.  Thus there could have been as many as 512 added operations.

I don't think there were 512, but I KNOW there were more than two.  Consider
all the instructions that used the IX and IY index registers - they all had
to be added opcodes...

The only fault to this shoehorning of all the new instructions into but two
opcodes was that all the USEFUL instructions took one additional cycle to
execute...

-- 
                    umd5.UUCP    <= {seismo!mimsy,ihnp4!rlgvax}!cvl!umd5!zben
Ben Cranston zben @ umd2.UMD.EDU    Kingdom of Merryland UniSys 1100/92
                    umd2.BITNET     "via HASP with RSCS"