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Apple provides multiple overlapping paging mechanisms which in total divide an Apple IIe's address space up into thirteen distinct segments.
Segments
0000–01FF
Reading and writing: contains auxiliary RAM if ALTZP is set. Contains base RAM otherwise.
0200–03FF; 0800–1FFF; 4000–BFFF
Reading: contains base RAM if RAMRD is reset; contains auxiliary RAM otherwise.
Writing: as per reading, but regarding RAMWRT rather than RAMRD.
0400–07FF
Reading: contains auxiliary RAM if either (i) both 80STORE and PAGE2 are set; or (ii) 80STORE is reset and RAMRD is set. Contains base RAM otherwise.
Writing: as per reading, but regarding RAMWRT rather than RAMRD.
2000–3FFF
Reading: contains auxiliary RAM if either (i) 80STORE, PAGE2 and HIRES are set; or (ii) 80STORE is reset and RAMRD is set. Contains base RAM otherwise.
Writing: as per reading, but regarding RAMWRT rather than RAMRD.
C000–C0FF
Never mapped to RAM or ROM. Always contains internal and card IO.
C100–C2FF; C400–C7FF
Contains ROM if RDCXROM is set. Otherwise is unmapped, allowing cards to respond.
C300–C3FF
Contains ROM if RDCXROM is set or SLOTC3ROM is reset. Otherwise is unmapped, allowing card 3 to respond.
C800–CFFF
Contains ROM if RDCXROM or RDC8ROM is set. Otherwise is unmapped, allowing cards to respond.
RDC8ROM is documented only implicitly; it is set by any access within the C3 page while SLOTC3ROM is reset. It is reset by an access to CFFF, or by system reset. This adheres to the standard contract with cards for this space: any card may claim this area upon an access to its ROM but must release it upon an access to CFFF.
D000–DFFF
Reading: contains ROM if the language card read flip flop is disabled. Contains base RAM if the flip flop is enabled and ALTZP is reset. Otherwise contains auxiliary RAM.
Writing: empty if the language card write flip flop is enabled. Contains base RAM if the flip flop is disabled and ALTZP is reset. Otherwise contains auxiliary RAM.
The portion of RAM accessed depends upon the language card's BANK2 flip flop.
E000–FFFF
As per D000—E000 except that BANK2 does not affect the portion of RAM exposed.
Language Card Control
The language card contains four flip flops: BANK2, read, write and prewrite.
BANK2
This selects which of two 4kb segments will appear in the region D000–DFFF; it is set directly by address line 3 upon any access of the language-card switches.
Read [enable]
This selects whether RAM or ROM will be read in the language card area. When it is enabled, RAM is read.
Any access with address line 0 = address line 1 enables RAM. Accesses where the two address lines are not equal enable ROM.
Write [disable]
This selects whether RAM will be written to by writes to the language card area. When it is disabled, RAM can be written to. So it acts like a write-protect switch.
It is reset if: (i) pre-write is set; and (ii) a read occurs to an odd address.
It is set if: a read occurs to an even address.
Otherwise it does not change value.
Pre-write
This switch affects the write flip flop; it is set to the value of address line 1 upon any access of the language-card switches, after any change to write has occurred.
Older Apple IIs
Prior to the IIe there was no auxiliary RAM. A single block of RAM up to 48kb exists from 0000 upwards.
Internal ROM is 12kb, so there is no mechanism for selecting between cards and ROM in the C000–CFFF region. That area is always used by cards only.
A language card can be fitted which enables an extra 16kb of RAM in an 8kb segment and two 4kb banks in the D000–FFFF region, as described above.
80-column cards
Neither the II nor the II+ has any internal hardware to support 80-column output. 80-column expansion cards were normally installed in slot 3 and accessed via their card ROM. The IIe's ability to page internal ROM in C300–C3FF only allows it to provide software compatibility with those cards.