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From: avery@puff.UUCP (Slippery Jim)
Newsgroups: net.micro.apple
Subject: Re: ROM to RAM
Message-ID: <934@puff.UUCP>
Date: Tue, 20-May-86 12:33:59 EDT
Article-I.D.: puff.934
Posted: Tue May 20 12:33:59 1986
Date-Received: Fri, 23-May-86 22:49:56 EDT
References: <203@neoucom.UUCP> <3440@reed.UUCP> <566@pucc.BITNET>
Distribution: net
Organization: U of Wisconsin CS Dept
Lines: 22

This will be fairly short, as compared to the last few articles on the subject.
They have pretty much explained it the way I would. One note about the
difference between a ][ or ][+ and a //e is that if, on a ][ or ][+, you have
the upper 12k occupied by read-only RAM (tweaking $c080), and you hit reset,
the apple uses the RAM's version of the reset vector ($FFFE,$FFFF I think,
but I don't have my manuals any more) and will jump to whatever's in those
addresses no matter what. This was used for some hard reset trapping in the
old days. The //e, on the other hand, replaces the RAM with the ROM monitor
and basic whenever you hit reset. The normal address to have in the reset
vector is a RAM address to jump to. I believe this address is in page 3.
There's another vector next to the reset vector in the rom of interest to 
some people -- the IRQ vector. This also normally holds a page 3 address,
which, I believe, on the ][+, promptly returns. I once wrote an interrupt
driven terminal program for the ][+ with the Novation Apple-Cat ][ modem 
which can actually run in the background! It was very simple, and it took over
half of the screen, but you could be on a BBS and be editing and debugging
a basic program at the same time! Not bad for a 6502 based micro, huh?
Just a couple of thoughts. If you must reply, please use this address:

{seismo,ihnp4,allegra,topaz}!uwvax!gumby!bambam!pebbles!avery

as I'm no longer on puff.