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From: clt@pur-phy.UUCP (Carrick Talmadge)
Newsgroups: net.micro.apple
Subject: Re: Language cards . . . (6502) (long)
Message-ID: <1360@pur-phy.UUCP>
Date: Mon, 25-Jun-84 13:04:56 EDT
Article-I.D.: pur-phy.1360
Posted: Mon Jun 25 13:04:56 1984
Date-Received: Thu, 28-Jun-84 02:33:29 EDT
Organization: Purdue University Physics Dept.
Lines: 105

[Take that, you filthy line eater!]

This is a bit long, but I thought it might be of general interest...

>How can you get the system let you write to the language card?
>
>I want to use it for a program and all I can manage to do is to load
> int basic into it(not what I want!).

Hopefully, the following will answer your questions:

			   Memory Organization
			   -------------------

The Ramcard has 16K of memory, but has an address space allowed for 
it (forgetting for the momment $C080-$C08F) of $D000-$FFFF, or 12K.
To "fit" the entire ram address space into this area, two 4K segments
of memory share the space from $D000-$DFFF.  When you select either
bank one or bank two, you automatically select one of the two 4K
segments plus the other 8K from $E000-$FFFF.  The figure below
illustrates this.

				_________________           $FFFF
				|		|
				|		|
				|		|
				|		|
				|_______________|           $F000
				|		|
				|		|
				|		|
				|		|
			________|_______________|________   $E000
			|		|		|
			|		|		|
			|    BANK 1	|     BANK 2	|
			|		|		|
			|_______________|_______________|   $D000


			Ram Selection/Deselection
			-------------------------

		ADDRESS		Action

		$C080		Read-Deselect Ram(Enable Rom).
				Write protect Ram

		$C081		Read-Deselect Ram. Two sucessive
				Reads write enables Ram.

		$C082		Read-Deselect Ram(Enable Rom).
				Write protect Ram

		$C083		Read-Select Ram.  Two sucessive
				Reads write enables Ram.

		$C084		(Decodes same as $C080).

		$C085		(Decodes same as $C081)

		$C086		(Decodes same as $C082).

		$C087		(Decodes same as $C083)

		$C088-$C08F     Same action as (ADDRESS-8),
				except selects/deselects
				Bank 1 of Ram.

Example:

;
;  RAMSET  
;       Sets up ram card for usage.  Note that it doesn't
;  	copy Basic Rom (excepting enough Rom for Hires graphics
;       routines).
;
RAMSET  LDA $C081
	LDA $C081     		Enable Ramcard for writing

;
; Next a macro to move from,to,length
; This copies the Rom from $F300-$FFFF to ram
;
	MOV $F300,$F300,$D00   

	LDA $C083
	LDA $C083		Finally fully enable second Bank of Ram
;				(Read enable as well as write enable).
				
--------------------

Source:  What's Where in the Apple by W.F. Luebbert (Micro Ink)

    Notice than you should use reads, rather than writes, as the latter
will give unpredictable results (a write will select a memory location
twice, but in rapid sucession, so that the ramcard will notice two
address selections only part of the time).

    Hope this helps some.

				Carrick Talmadge

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