Caple C871i Manual do Utilizador descarregar pdf (Página 11)

100

101

Apple II Computer Info

diagnostic routines and some monitor extensions.

The SLOTC3/INTC3 switch determines whether $C300-$C3FF access slot ROM

space or the internal ROM. The $C800-$CFFF space is tied into this to

some extent, following the normal rules for the IOSEL soft switch. The

internal ROM in these areas contains the 80-column firmware.

The 80-column video modes are implemented by overlaying main and

auxiliary memory buffers, with the hardware reading simultaneously from

main and auxiliary memory and outputting data at twice the rate. For

each line, bytes alternate between main and auxiliary memory, with the

first byte coming from auxiliary memory.

In addition to 80-column text mode, there is a "double lo-res" mode and

a "double hi-res" mode. These aren't supported by firmware in the IIe.

(The IIgs does support double lo-res mode in Applesoft BASIC.)

The double resolution modes have two video buffers, but it is harder to

use the second page, since there are no bank switching methods to toggle

the $0800-$0BFF and $4000-$5FFF areas except the RAMRD/RAMWR switch. In

addition, you cannot display page 2 while the 80STORE switch is enabled,

since the PAGE1/2 switch becomes a bank selector and the video hardware

always displays page 1.

The primary character set is the same as the ][+ with the addition of

normal lower case characters: $00-$3F are inverse, $40-$7F are flashing,

$80-$9B are control characters (display as normal) and $A0-$FF are

normal, including lower cases.

The alternate character set is used by the 80-column firmware. It

disables flashing, and replaces the $60-$7F range with inverse lower

case characters. The $40-$5F range have two implementations: in the

original IIe they are inverse upper case (identical to $00-$1F), and in

the enhanced IIe (and the IIc and IIgs) they are mousetext characters.

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Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 11 of 572

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