Apple ][+

Open 8bitworkshop IDE

Click here to program the Apple II in the 8bitworkshop IDE now!

Apple ][+ Specifications

Lifespan

1979-1983

Media

Cassette tape, 5.25” floppy disk (Disk II)

CPU

MOS Technology 6502 @ 1 MHz

Memory

16K-48K RAM, 12K ROM (expandable to 64K with a Language Card)

Display

40x24 text, 40x48 lo-res graphics (16 colors), 280x192 hi-res graphics (6 colors)

Sound

1-bit speaker

Input

Keyboard, paddle controllers, joystick

History

The Apple ][+ was introduced by Apple Computer, Inc. in June 1979 as an enhancement to the original Apple ][ model, which was released in 1977. The Apple ][ series of computers were designed primarily by Steve Wozniak and marketed by Steve Jobs. The Apple ][+ added the Applesoft BASIC programming language, which was integrated into the ROM and replaced the Integer BASIC of the original Apple ][. The Apple ][+ also featured an improved keyboard, with keys for control characters and lowercase letters.

The Apple ][+ was successful in the early years of personal computing, especially in the education market. It was eventually succeeded by the Apple //e in 1983, which replaced the discrete IC-based circuitry with a single ASIC chip.

Programming

Applesoft BASIC was developed by Microsoft. It offered improved floating-point arithmetic and graphics commands compared to Integer BASIC. On an unexpanded Apple ][+, Integer BASIC is no longer available; it can be restored by loading it into RAM on an optional Language Card (the same card that provides the bank-switched RAM described below).

The 8bitworkshop IDE doesn’t include the original Apple ROMs, so BASIC is not available. Instead, you can program in 6502 assembler or in C with the CC65 compiler tools.

Memory Map

Address Range	Description
$0000-$00FF	Zero page
$0100-$01FF	Stack
$0200-$02FF	Input buffer, variables
$0300-$03BF	Free space
$03C0-$03FF	DOS Vectors
$0400-$07FF	Text/Lores Page 1
$0800-$1FFF	Free space
$2000-$3FFF	Hires Page 1
$4000-$5FFF	Hires Page 2
$6000-$BFFF	Free space
$C000-$CFFF	I/O switches and slot ROM
$D000-$DFFF	ROM (or bank-switched RAM bank 1/2 with Language Card)
$E000-$FFFF	ROM (Applesoft BASIC, Monitor), or RAM with Language Card

I/O Switches and Softswitches

The Apple ][+ uses memory-mapped I/O with “softswitches” - reading or writing (or in some cases just accessing, read or write) specific memory addresses toggles hardware features. Note that the 80-column/auxiliary-memory switches found at $C000-$C00F on the later Apple //e (80STORE, RAMRD, RAMWRT, ALTZP, SLOTC3ROM, 80COL, ALTCHARSET, INTCXROM) don’t exist on the ][+ - on this machine $C000 and $C010 are the keyboard data and strobe registers instead.

Address	Function
$C000	Keyboard data (read); bit 7 set if a key has been pressed, bits 0-6 are the ASCII code
$C010	Keyboard strobe (read or write clears the keyboard strobe / “any key down” flag)
$C020	Cassette output toggle
$C030	Speaker toggle
$C040	Utility strobe (game I/O connector)
$C050	Graphics mode
$C051	Text mode
$C052	Mixed graphics/text off
$C053	Mixed graphics/text on
$C054	Text/graphics page 1
$C055	Text/graphics page 2
$C056	Lo-res graphics
$C057	Hi-res graphics
$C058	Annunciator 0 off
$C059	Annunciator 0 on
$C05A	Annunciator 1 off
$C05B	Annunciator 1 on
$C05C	Annunciator 2 off
$C05D	Annunciator 2 on
$C05E	Annunciator 3 off
$C05F	Annunciator 3 on
$C060	Cassette input
$C061	Push button 0 (open-apple / PB0)
$C062	Push button 1 (closed-apple / PB1)
$C063	Push button 2 (PB2)
$C064	Paddle 0 analog input (PDL0)
$C065	Paddle 1 analog input (PDL1)
$C066	Paddle 2 analog input (PDL2)
$C067	Paddle 3 analog input (PDL3)
$C070	Paddle trigger (resets paddle RC timers)
$C080-$C08F	Language Card bank switching (see below)
$C0S0-$C0SF	Slot I/O (peripheral card soft switches; S = slot number 1-7)

Language Card Bank Switching ($C080-$C08F)

A 16K Language Card in slot 0 (or the equivalent built-in RAM on later machines) adds two extra 4K RAM banks that can be swapped in under the $D000-$DFFF ROM area, plus 8K of RAM that lives under $E000-$FFFF. Access to $D000-$DFFF is controlled by bit 3 of the address (bank 1 vs. bank 2); access to $E000-$FFFF always uses the same RAM regardless of which bank is selected. The switches are accessed by reading (not writing) the following addresses; writing is enabled only after the switch has been read twice in a row:

Address	Read source ($D000-$FFFF)	Write
$C080	RAM bank 2	Write-protected
$C081	ROM	RAM bank 2 (after 2 reads)
$C082	ROM	Write-protected
$C083	RAM bank 2	RAM bank 2 (after 2 reads)
$C088	RAM bank 1	Write-protected
$C089	ROM	RAM bank 1 (after 2 reads)
$C08A	ROM	Write-protected
$C08B	RAM bank 1	RAM bank 1 (after 2 reads)

$C084-$C087 mirror $C080-$C083, and $C08C-$C08F mirror $C088-$C08B.

Typical usage:

• To run code from language-card RAM, read $C081 (or $C089 for bank 1) twice to select ROM-read/RAM-write, copy your code/data into $D000-$FFFF, then read $C080/$C088 once to switch back to reading RAM with writes disabled.

• DOS 3.3 and ProDOS both relocate parts of themselves into language-card RAM using this mechanism to free up main memory.

Graphics Modes

Text Mode (40x24)

Standard text display using the built-in character set. Characters are stored in the text page starting at $0400.

Lo-Res Graphics (40x48, 16 colors)

Low-resolution color graphics with 16 available colors. Each byte represents two 4-bit pixels vertically stacked.

Hi-Res Graphics (280x192, 6 colors)

High-resolution monochrome graphics with color artifacts. Uses two graphics pages at $2000 and $4000.

Development Tools

CC65 Compiler

C programs are compiled using the CC65 toolchain, which provides:

• Standard C library support

• Apple II-specific extensions

• TGI (Tiny Graphics Interface) graphics library

• Conio (console I/O) library

Assembly Tools

• DASM - Versatile macro assembler (.a, .dasm)

• Merlin32 - Apple II-specific assembler (.lnk)

• CA65 - CC65’s linker-aware assembler (.s, .ca65)

Memory Configuration

Programs that use hi-res graphics should include the following:

#define CFGFILE apple2-hgr.cfg
#pragma data-name(push,"HGR")
#pragma data-name(pop)

For details and other configuration files, see the CC65 documentation.

Binary Formats

The 8bitworkshop Apple II platform detects multiple binary formats for loading programs:

Disk Images (.dsk files)

• 16-sector, 35-track disk images (143,360 bytes)

• Automatically detected and mounted as a DiskII drive in slot 6

• Supports Apple DOS 3.3 format with multiple files

AppleSingle Format

• Header signature: $00 $05 $16 $00 (first 4 bytes)

• Load address: Stored at offset $38-$39 (big-endian)

• Header size: 58 bytes

• Used by CC65 compiler (exehdr.s)

DOS 3.3 Binary Format

• 4-byte header: origin address (2 bytes, little-endian) + size (2 bytes, little-endian)

• Automatically detected when:

  • Size matches file length minus 4 bytes

  • Origin address is less than $C000

  • Origin + size is less than $13000

  • Origin is $803 or aligned to $xx00

• Programs load at the specified origin address in the header

Raw Binary Format

• Default load address: $803

• Used when no other format is detected

Helpful Links

• PEEKs and POKEs

• Apple II Programming Reference

• CC65 Compiler Documentation

• 6502 Assembly Language Programming

Comments