Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!bbn!drilex!dricejb
From: dricejb@drilex.UUCP (Craig Jackson drilex1)
Newsgroups: comp.arch
Subject: Re: PUSH on i8088/i80x86
Message-ID: <7296@drilex.UUCP>
Date: 6 Jan 90 16:35:08 GMT
References: <182DAVISTD@MSU>
Organization: DRI/McGraw-Hill, Lexington, MA
Lines: 25

In article <182DAVISTD@MSU> DAVISTD@MSU.BITNET (Tom Davis) writes:
<In debugging some vendor code (:-) I came across what appears to be a subtle
<difference between the i8088 and i80x86.  Without an i80x86 manual handy, I
<wondered if someone could verify my claim...
<
<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).
<Therefore, on the i8088 the following code does not work as expected:
<
<  PUSH SP
<  POP  SP
<
<(SP ends up "off by two bytes".)
<-------
<Tom Davis                 | The above statement shall be construed,
<Network Software Services | interpreted, and governed by me alone.
<Michigan State University | EMail: davistd@ibm.cl.msu.edu

The behavior of "PUSH SP" was one of the documented differences between the
808[68] and its succcessors... this should be documented in an 80186 or
80286 manual.
-- 
Craig Jackson
dricejb@drilex.dri.mgh.com
{bbn,axiom,redsox,atexnet,ka3ovk}!drilex!{dricej,dricejb}