Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uunet!mcsun!ukc!strath-cs!cs.glasgow.ac.uk!bru-cc!md89mch
From: md89mch@cc.brunel.ac.uk (Martin Howe)
Newsgroups: comp.arch
Subject: Re: PUSH on i8088/i80x86
Message-ID: <1244@Terra.cc.brunel.ac.uk>
Date: 10 Jan 90 23:55:30 GMT
References: <182DAVISTD@MSU> <5524@bd.sei.cmu.edu>
Reply-To: md89mch@cc.brunel.ac.uk (Martin Howe)
Organization: Dept. of EE &E, Brunel University, Uxbridge, UK
Lines: 24

In article <5524@bd.sei.cmu.edu> firth@sei.cmu.edu (Robert Firth) writes:

>>On the i8088, a "PUSH SP" decrements SP before pushing it onto the stack.  On
>>the i80x86, SP is pushed onto the stack before it is decremented (somehow).

In the iAPX-286 manual, I remember it saying that the 802[and presumable 34]86
pushes a DIFFERENT value for SP onto the stack from that pushed by the
8086/8088. I don't know about the 186 and I've never heard of any 8086/8088
difference, since they have the same execution units.

On a '286, though
	PUSH BP
	MOV  BP,SP
	XCHG BP,[BP]
is supposed to emulate the behaviour of the 8086/8088's PUSH SP, 
at least according to Intel.

I hope this helps.
Regards,
-- 
Martin C. Howe           | "Motorhead will be the DIRTIEST band in
MSc. Microelectronics    |  Rock N' Roll. If this band moved in next door,
System Design, Brunel U. |  your lawn would die." - Kilminster
Any unattributed opinions are mine, but YOU can have them today for just $20 !