Path: utzoo!attcan!uunet!lll-winken!ames!hc!pprg.unm.edu!unmvax!tut.cis.ohio-state.edu!ucbvax!UIAMVS.BITNET!AWCTTYPA
From: AWCTTYPA@UIAMVS.BITNET ("David A. Lyons")
Newsgroups: comp.sys.apple
Subject: RESET vector, Ctrl-Y vector, etc.
Message-ID: <8904102042.aa02599@SMOKE.BRL.MIL>
Date: 10 Apr 89 22:30:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 33

>Date:         Fri, 7 Apr 89 19:01:49 GMT
>From:         Bevan Wang <marque!carroll1!acct015@CSD4.MILW.WISC.EDU>
>Subject:      Vectors...
>
>Does anyone know how the Reset vector works?  And why the values differ
>in ProD[OS] and DOS 3.3?  Also what the heck is the USER Control-Y vector,
>the Non-maskable interrupt vector?

The system jumps through the reset vector ($3F2-3) after cleaning
things up when Reset is pressed.  If the power-up byte at $3F4 is
not $3F3 EOR #$A5, then the system reboots instead.

ProDOS doesn't fiddle with the RESET vector itself:  its value
depends on what SYS program you're using (BASIC.SYSTEM, for
example).

The Ctrl-Y vector at $3F8-A should be a JMP.  It is called by the
Ctrl-Y command in the monitor.  The NMI vector at $3FB-D is called
when an NMI occurs--it should be a JMP, too.  No Apple machines make
use of the NMI, but you can attach a wire and a pushbutton to it
yourself if you really feel like it.  (Don't attempt to return from
an NMI, though, and be careful--you could mess up a disk by
interrupting at the wrong time.)

>Bevan R.S. Wang
>acct015@carroll1.UUCP

 --David A. Lyons              bitnet: awcttypa@uiamvs
   DAL Systems                 CompuServe:  72177,3233
   P.O. Box 287                GEnie mail:    D.LYONS2
   North Liberty, IA 52317     AppleLinkPE: Dave Lyons
   (Watch this space!  New U.S. mail address & net address
    will appear.)