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Apple ][
The bulk of this page will focus on the Enhanced IIe, both because it was the most popular of the line and because it is the model we have.
Memory layout
Despite the 6502's 64K address space, an Apple II could have significantly more RAM and ROM than that. The IIe came standard with 64K built into the motherboard, which could be doubled with an extended 80-column text card. Other peripheral cards tended to contain their own onboard RAM/ROM. All of this extra memory is accessible through bank switching.
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\$0000–\$00FF: zero page
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\$0100–\$01FF: stack, Applesoft temporary storage
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\$0200–\$02FF: keyboard/diskette input buffer
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\$0300–\$03CF: user assembly programs
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\$03D0–\$03FF: subroutine vectors for DOS, Applesoft, and system monitor
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\$0400–\$07FF: text/low-res page 1
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\$0800–\$0BFF: text/low-res page 2; more commonly used for Applesoft program storage
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\$0C00–\$1FFF: free for use
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\$2000–\$3FFF: high-res page 1
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\$4000–\$5FFF: high-res page 2
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\$6000–\$BFFF: normally free for use; \$9600 and above is used by DOS
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\$C000–\$C0FF: I/O
Zero page
I/O
Table 1: Soft switches, status, and I/O addresses [1]
| Address | Direction | Symbolic name | Description |
|---|---|---|---|
| \$C000 | W | 80STOREOFF | Allow PAGE2 to switch between video page 1 and page 2 |
| R | KBD | Keyboard data (bits 0–6) | |
| R7 | KBD | 1 = keyboard stroke is on 0 = keyboard stroke is off |
|
| \$C001 | W | 80STOREON | Allow PAGE2 to switch between main and aux video memory |
| \$C002 | W | RAMRDOFF | Read-enable main memory from \$0200–\$BFFF |
| \$C003 | W | RAMRDON | Read-enable aux memory from \$0200–\$BFFF |
| \$C004 | W | RAMWRTOFF | Write-enable main memory from \$0200–\$BFFF |
| \$C005 | w | RAMWRTON | Write-enable aux memory from \$0200–\$BFFF |
| \$C006 | W | INTCXROMOFF | Enable slot ROM from \$C100–\$CFFF |
| \$C007 | W | INTCXROMON | Enable main ROM from \$C100–\$CFFF |
| \$C008 | W | ALTZPOFF | Enable main memory from \$0000–\$01FF and make main BSR available |
| \$C009 | W | ALTZPON | Enable aux memory from \$0000–\$01FF and make aux BSR available |
| \$C00A | W | SLOTC3ROMOFF | Enable main ROM from \$C300–\$C3FF |
| \$C00B | W | SLOTC3ROMON | Enable slot ROM from \$C300–\$C3FF |
| \$C00C | W | 80COLOFF | Turn off 80-column display |
| \$C00D | W | 80COLON | Turn on 80-column display |
| \$C00E | W | ALTCHARSETOFF | Turn off alternate characters |
| \$C00F | W | ALTCHARSETON | Turn on alternate characters |
| \$C010 | R7 | AKD | 1 = a key is being pressed 0 = all keys are released |
| RW | KBDSTRB | Clear keyboard strobe | |
| \$C011 | R7 | BSRBANK2 | 1 = bank 2 of BSR is available 0 = bank 1 of BSR is available |
| \$C012 | R7 | BSRREADRAM | 1 = BSR is active for read operations 0 = \$D000–\$FFFF ROM is active for read operations |
| \$C013 | R7 | RAMRD | 0 = main \$0200–\$BFFF is active for read operations 1 = aux \$0200–\$BFFF is active for read operations |
| \$C014 | R7 | RAMWRT | 0 = main \$0200–\$BFFF is active for write operations 1 = aux \$0200–\$BFFF is active for write operations |
| \$C015 | R7 | INTCXROM | 1 = main \$C100–\$CFFF ROM is active 0 = slot \$C100–\$C1FF ROM is active |
| \$C016 | R7 | ALTZP | 1 = aux zero page & stack are active; aux BSR is available 0 = main zero page & stack is active; main BSR is available |
| \$C017 | R7 | SLOTC3ROM | 1 = slot \$C3 ROM is active 0 = main \$C3 ROM is active |
| \$C018 | R7 | 80STORE | 1 = PAGE2 switches main/aux 0 = PAGE2 switches video pages |
| \$C019 | R7 | VERTBLANK | 1 = vertical retrace is on 0 = vertical retrace is off |
| \$C01A | R7 | TEXT | 1 = a text mode is active 0 = a graphics mode is active |
| \$C01B | R7 | MIXED | 1 = mixed graphics and text 0 = full-screen graphics |
| \$C01C | R7 | PAGE2 | 1 = video page 2 selected OR aux video page selected |
| \$C01D | R7 | HIRES | 1 = high-res graphics 0 = low-res graphics |
| \$C01E | R7 | ALTCHARSET | 1 - alternate character set is on 0 = primary character set is on |
| \$C01F | R7 | 80COL | 1 = 80-column display is on 0 = 40-column display is on |
| \$C020 | R | CASSOUT | Toggle the state of the cassette output port |
| \$C021 | |||
| \$C022 | |||
| \$C023 | |||
| \$C024 | |||
| \$C025 | |||
| \$C026 | |||
| \$C027 | |||
| \$C028 | |||
| \$C029 | |||
| \$C02A | |||
| \$C02B | |||
| \$C02C | |||
| \$C02D | |||
| \$C02E | |||
| \$C02F | |||
| \$C030 | R | SPEAKER | Toggle the state of the speaker |
| \$C031 | |||
| \$C032 | |||
| \$C033 | |||
| \$C034 | |||
| \$C035 | |||
| \$C036 | |||
| \$C037 | |||
| \$C038 | |||
| \$C039 | |||
| \$C03A | |||
| \$C03B | |||
| \$C03C | |||
| \$C03D | |||
| \$C03E | |||
| \$C03F | |||
| \$C040 | R | GCSTROBE | Generate a game I/O connector strobe signal |
| \$C041 | |||
| \$C042 | |||
| \$C043 | |||
| \$C044 | |||
| \$C045 | |||
| \$C046 | |||
| \$C047 | |||
| \$C048 | |||
| \$C049 | |||
| \$C04A | |||
| \$C04B | |||
| \$C04C | |||
| \$C04D | |||
| \$C04E | |||
| \$C04F | |||
| \$C050 | RW | TEXTOFF | Select graphics mode |
| \$C051 | RW | TEXTON | Select text mode |
| \$C052 | RW | MIXEDOFF | Use full screen for graphics |
| \$C053 | RW | MIXEDON | User graphics with four lines of text |
| \$C054 | RW | PAGE2OFF | Select page 1 display (or main video memory) |
| \$C055 | RW | PAGE2ON | Select page 2 display (or aux video memory) |
| \$C056 | RW | HIRESOFF | Select low-res graphics |
| \$C057 | RW | HIRESON | Select high-res graphics |
| \$C058 | RW | CLRAN0 | Turn off annunciator 0 |
| \$C059 | RW | SETAN0 | Turn on annunciator 0 |
| \$C05A | RW | CLRAN1 | Turn off annunciator 1 |
| \$C05B | RW | SETAN1 | Turn on annunciator 1 |
| \$C05C | RW | CLRAN2 | Turn off annunciator 2 |
| \$C05D | RW | SETAN1 | Turn on annunciator 2 |
| \$C05E | RW | CLRAN3 | Turn off annunciator 3 |
| \$C05F | RW | SETAN1 | Turn on annunciator 3 |
| \$C060 | R7 | CASSIN | 1 = cassette input is on |
| \$C061 | R7 | PB0 | 1 = push button 0 is on |
| \$C062 | R7 | PB1 | 1 = push button 1 is on |
| \$C063 | R7 | PB2 | 1 = push button 2 is on |
| \$C064 | R7 | GC0 | 0 = game controller 0 timed out |
| \$C065 | R7 | GC1 | 0 = game controller 1 timed out |
| \$C066 | R7 | GC2 | 0 = game controller 2 timed out |
| \$C067 | R7 | GC3 | 0 = game controller 3 timed out |
| \$C068 | R | GCRESET | Reset the game controllers |
| \$C069 | |||
| \$C06A | |||
| \$C06B | |||
| \$C06C | |||
| \$C06D | |||
| \$C06E | |||
| \$C06F | |||
| \$C070 | |||
| \$C071 | |||
| \$C072 | |||
| \$C073 | |||
| \$C074 | |||
| \$C075 | |||
| \$C076 | |||
| \$C077 | |||
| \$C078 | |||
| \$C079 | |||
| \$C07A | |||
| \$C07B | |||
| \$C07C | |||
| \$C07D | |||
| \$C07E | |||
| \$C07F | |||
| \$C080 | R | READBSR2 | Select bank 2, read BSR, write-protect BSR |
| \$C081 | RR | WRITEBSR2 | Select bank 2, read ROM, write-enable BSR |
| \$C082 | R | OFFBSR2 | Select bank 2, read ROM, write-protect BSR |
| \$C083 | RR | RDWRBSR2 | Select bank 2, read BSR, write-enable BSR |
| \$C084 | |||
| \$C085 | |||
| \$C086 | |||
| \$C087 | |||
| \$C088 | R | READBSR1 | Select bank 1, read BSR, write-protect BSR |
| \$C089 | RR | WRITEBSR1 | Select bank 1, read ROM, write-enable BSR |
| \$C08A | R | OFFBSR1 | Select bank 1, read ROM, write-protect BSR |
| \$C08B | RR | RDWRBSR1 | Select bank 1, read BSR, write-enable BSR |
| \$C08C | |||
| \$C08D | |||
| \$C08E | |||
| \$C08F | |||
| \$C090–\$C09F | Reserved for use by slot 1 | ||
| \$C0A0–\$C0AF | Reserved for use by slot 2 | ||
| \$C0B0–\$C0BF | Reserved for use by slot 3 | ||
| \$C0C0–\$C0CF | Reserved for use by slot 4 | ||
| \$C0D0–\$C0DF | Reserved for use by slot 5 | ||
| \$C0E0–\$C0EF | Reserved for use by slot 6 | ||
| \$C0F0–\$C0FF | Reserved for use by slot 7 |
Video memory
Programming
Applesoft
Integer BASIC
System monitor
Operating systems
DOS 3.3
ProDOS 8
CP/M
Resources
References
[1]
Inside the Apple IIe (1985)