Caple C871i Bedienungsanleitung PDF herunterladen (Seite 281)

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101

Apple II Computer Info

example. However, for memory in $0000...$01FF and $D000...$FFFF, reading

and writing are not separately selectable...you either read and write in

the main bank, or you read and write in the aux bank.

Looks simple enough, doesn't it? Well, here comes the complicated part.

There is another switch that affects bank switching:

$C000: Turn off 80-column bank switching

$C001: Turn on 80-column bank switching

(As above, these switches must be accessed by writing.)

If 80-column bank switching is off, bank switching works exactly as

described above. But if 80-column bank switching is on, the text screen

($0400...$07FF) becomes immune to the normal bank-switching controls. In

this mode, the text screen is bank-switched by the following controls

instead:

$C054: Map the main text page into $0400...$07FF

$C055: Map the aux text page into $0400...$07FF

(These switches can be triggered by ANY access, not just a write.)

Note that this is the PAGE1/PAGE2 switch. When 80-colunn bank switching

is on, text page 2 (and graphics page 2) cannot be displayed.

As if that weren't confusing enough, turning on the HIRES switch (by

accessing $C057) causes hires page 1 ($2000...$3FFF) to behave just like

the text screen--it too becomes immune to the normal bank-switching

controls, and is switched instead by $C054, $C055.

Actually, I lied when I wrote above that the I/O area ($C000...$CFFF)

doesn't bank-switch. The following switches control portions of this

memory area:

$C006: Map slot card ROMs into $C100...$CFFF

$C007: Map internal ROM into $C100...$CFFF

$C00A: Map built-in 80-column firmware into $C300...$C3FF

$C00B: Map slot card ROM into $C300...$C3FF

(These are write-only switches.)

- Neil Parker

Neil Parker, nparker@{cie-2,cie}.uoregon.edu, http://cie-2.uoregon.edu/~nparker

"Bad move, Neil!" -- The Tick

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From: [email protected] (David Empson)

Subject: Re: memory switches

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Date: Wed, 8 Nov 1995 15:11:06 GMT

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Apple II Computer Technical Information : Apple II Family Hardware Info

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