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Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!inuxc!pur-ee!CS-Mordred!Pucc-H:Pucc-I:ags
From: ags@pucc-i (Seaman)
Newsgroups: net.micro.apple
Subject: Re: Language cards (AKA bank-switched memory)
Message-ID: <337@pucc-i>
Date: Tue, 3-Jul-84 02:14:51 EDT
Article-I.D.: pucc-i.337
Posted: Tue Jul  3 02:14:51 1984
Date-Received: Wed, 4-Jul-84 03:25:52 EDT
References: <1360@pur-phy.UUCP> <2869@utah-cs.UUCP>
Organization: Purdue University Computing Center
Lines: 22

>  If one writes to an address between $D000 and $FFFF, and the card has not 
>  been selected (and has not been write protected), the write is still done 
>  on the language card.  Of course, to read the card one has to select it.

This is the basis for an easy way to copy the F8 ROM into RAM (I'll just do
one byte):

	LDA	$C081	;Enable ROM read
	LDA	$C081	; and RAM write (must do it twice)
	LDA	$FFFF	;this fetches from ROM
	STA	$FFFF	;this stores in RAM

Voila!  Write-only memory!

An even easier way on the //e is to call the routine COPYROM at $CF78.
Notice that there is no language card on a //e.  The upper 16K is simply 
called "bank-switched memory," a curious term since ALL the memory on a 
128K //e is bank-switched.
-- 

Dave Seaman			"My hovercraft is full of eels."
..!pur-ee!pucc-i:ags