Caple C871i Manual do Utilizador descarregar pdf (Página 283)

Apple II Computer Info

The IIe-specific soft switches all use three I/O locations. A pair of

locations set the soft switch to the "on" and "off" states by writing

to the location (value is irrelevant). The third location allows

software to read the current state of the switch, by examining bit 7

of the returned value (the switch is "on" if bit 7 is set).

The softswitches related to auxiliary memory bank switching are as

follows:

Name OFF location ON location READ location

RAMRD $C002 (write) $C003 (write) $C013 (read bit 7)

RAMWR $C004 (write) $C005 (write) $C014 (read bit 7)

ALTZP $C008 (write) $C009 (write) $C016 (read bit 7)

80STORE $C000 (write) $C001 (write) $C018 (read bit 7)

PAGE2 $C054 (r/w) $C055 (r/w) $C01C (read bit 7)

AN3 $C05E (r/w) $C05F (r/w) not available

The RAMRD switch determines which bank is accessed for READ operations

in the address range $0200 to $BFFF. If this switch is OFF, main

memory is read. If this switch is ON, auxiliary memory is read.

The RAMWR switch determines which bank is accessed for WRITE operations

in the address range $0200 to $BFFF. If this switch is OFF, main

memory is written. If this switch is ON, auxiliary memory is written.

The ALTZP switch determines which bank is accessed for both READ and

WRITE operations in the address ranges $0000 to $01FF (zero page and

stack memory) and $D000 to $FFFF ("language card"). If this switch is

OFF, main memory is accessed. If this switch is ON, auxiliary memory

is accessed.

In addition to these three switches, there are special facilities to

simplify access to the 80-column text buffer (half of which is in

auxiliary memory at $0400-$07FF) and first page of the double hi-res

graphics buffer (half of which is in auxiliary memory at $2000-$3FFF).

These facilities are controlled by the 80STORE switch. If 80STORE is

OFF, then auxiliary memory switching is controlled only by the RAMWR

and RAMWR switches.

If 80STORE is ON, then the PAGE2 switch controls the bank accessed in

the $0400-$07FF area. If PAGE2 is OFF, main memory is accessed. If

PAGE2 is ON, auxiliary memory is accessed. This overrides the current

setting of RAMRD and RAMWR.

Note: PAGE2 normally selects the displayed text or graphics page (1 or

2). This function is disabled while 80STORE is active, and only page 1

can be displayed.

Note also that the 80STORE bank switching function is independent of

the display of 80-column text and double hi-res graphics mode, which

involves the 80COL soft switch ($C00C write = OFF, $C00D write = ON,

$C01F = read).

The AN3 switch is involved in the use of double hi-res graphics mode.

If AN3 is OFF ($C05E), double hi-res graphics is ENABLED. Double

hi-res graphics will also be displayed if 80COL is ON and HIRES

($C057) is ON.

Apple II Computer Technical Information : Apple II Family Hardware Info

ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 283 of 572

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