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From: rhyde@ucrmath.ucr.edu (randy hyde)
Newsgroups: comp.sys.apple2
Subject: Re: MMu on the IIgs
Message-ID: <11148@ucrmath.ucr.edu>
Date: 15 Jan 91 07:03:02 GMT
References: <278d0eda.563e@petunia.CalPoly.EDU> <1991Jan11.065402.640@ux1.cso.uiuc.edu> <91011.085913AABENSON@MTUS5.BITNET>
Organization: University of California, Riverside
Lines: 15

>>>>>
Okay, I've heard it said a couple times.  Orca uses COP for software
interrupts.  Why is this?  I think BRK would have been a better choice.
<<<<<

Software debuggers use the BRK instruction.
Bill Mensch originally intended the COP instruction to be used for two
purpose-- as a software interrupt (exactly like Byteworks is using it)
and as a mechanism to extend the instruction set.  Note that COP is a
two byte instruction with the second byte being an immediately value.
If you read the '816 data sheet closely, you'll note that Mensch reserved
certain opcodes following the COP.  This, apparantly, was for opcode
expansion.  If someone out there has the specs on the 832 they should post
a message describing if (and how) Bill Mensch put these opcodes to work.
*** Randy Hyde