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Apple II Computer Info

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Path: news.uiowa.edu!chi-news.cic.net!news.uoregon.edu!cie-2.uoregon.edu!nparker

From: [email protected] (Neil Parker)

Newsgroups: comp.sys.apple2

Subject: Re: memory switches

Date: 8 Nov 1995 09:20:23 GMT

Organization: University of Oregon Campus Information Exchange

Lines: 87

Message-ID: <[email protected]>

References: <[email protected]>

NNTP-Posting-Host: cie-2.uoregon.edu

In article <[email protected]>

[email protected] (John Edward Flanders) writes:

>Could anyone please explain the locations and functions of the memory bank

>switches on an Apple //e with 128k memory?

Have patience...this gets rather complicated.

The bank-switching controls are as follows:

$C002: Select main memory for reading in $0200...$BFFF

$C003: Select aux memory for reading in $0200...$BFFF

$C004: Select main memory for writing in $0200...$BFFF

$C005: Select aux memory for reading in $0200...$BFFF

$C008: Select main memory for reading & writing in $0000...$01FF & $D000...$FFFF

$C009: Select aux memory for reading & writing in $0000...$01FF & $D000...$FFFF

To activate any switch, write a value at the I/O location. It doesn't matter

what you write; the act of writing is what triggers the switch. (You *must*

access the switch by writing--reading a switch just gets you the ASCII code

of the most recent keypress, and doesn't do any bank switching.)

Don't ever try to POKE these switches from BASIC--you'll bank-switch yourself

out of existence.

Note that these switches divide memory into four ranges:

$0000...$01FF: Switched by $C008, $C009.

$0200...$BFFF: Switched by $C002...$C005.

$C000...$CFFF: Not switchable.

$D000...$FFFF: Switched by $C008, $C009. This is the "language card"

area...the switch only controls which of the two

"language cards" (main or aux) is active...if you

have ROM mapped into this area, it never switches (i.e.

there's only one ROM, and it shows up in both the main

and aux banks).

Note that for memory in $0200...$BFFF, reading and writing are separately

selectable...you can read from main memory and write to aux memory, for

Apple II Computer Technical Information : Apple II Family Hardware Info

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