Apple II

The Apple II (1977) was one of the first mass-market personal computers and one of the longest-lived — the Apple II line remained in production until 1993. Designed by Steve Wozniak, it introduced many features that became standard: colour graphics, a built-in BASIC interpreter, expansion slots, and a floppy disk drive.

The IDE supports the Apple ][+ and Apple //e models, which are the most common targets for homebrew development.

Languages in the IDE

Language	Notes
CC65 C	C cross-compiler with Apple II target library
6502 assembly	ca65 assembler (part of the cc65 suite)
AppleSoft BASIC	Built into ROM — available at the `]` prompt

Quick start

Select Apple ][+ or Apple //e as the platform.
Choose your language preset.
The IDE loads an Apple II emulator (typically based on AppleWin or a JS emulator).
Build and run.

The ] prompt

The Apple II boots directly to AppleSoft BASIC — the ] prompt. Machine code programs are called from BASIC using CALL address or from the monitor with address G. The IDE template handles this automatically.

Hardware overview

CPU — MOS 6502 at 1 MHz

The Apple II uses the same 6502 as the C64 and BBC Micro, running at 1.023 MHz. See 6502 assembly for the full instruction set.

The Apple //e uses the 65C02 (an enhanced 6502) — same instruction set plus a handful of new instructions (STZ, TRB, TSB, PHX, PHY, etc.). CC65 and ca65 support both.

Video — Woz's Video Hardware

Apple II video is driven by cleverly timing the CPU's memory accesses. It supports several modes:

Mode	Resolution	Colours	Notes
Text	40×24 characters	Green/amber/white on black	ROM character set
Lo-Res	40×48 "blocks"	16 colours	Chunky pixels from text page
Hi-Res	280×192 pixels	6 colours*	Famous "HIRES" mode
Double Hi-Res (//e)	560×192	16 colours	Requires 80-col card

*Hi-Res colour is quirky — colour depends on the horizontal position of pixels, not just the byte value. Pairs of pixels form colour dots. This leads to Apple II's characteristic colour-fringing look.

Memory map

Range	Contents
$0000–$00FF	Zero page
$0100–$01FF	Stack
$0200–$02FF	Input buffer
$0300–$03FF	System vectors and I/O
$0400–$07FF	Text page 1 / Lo-Res page 1
$0800–$0BFF	Text page 2 / Lo-Res page 2
$2000–$3FFF	Hi-Res page 1 (8 KB)
$4000–$5FFF	Hi-Res page 2 (8 KB)
$6000–$95FF	Free RAM (on 48K machine)
$C000–$C0FF	Soft switches (I/O)
$C100–$CFFF	Peripheral card ROMs
$D000–$DFFF	DOS / ProDOS area
$E000–$FFFF	ROM (BASIC, Monitor)

Soft switches

The Apple II uses soft switches — memory addresses in $C000–$C0FF that toggle hardware modes when read or written:

Address	Action
$C050	Graphics mode on
$C051	Text mode on
$C052	Full-screen graphics
$C053	Mixed mode (text at bottom)
$C054	Display page 1
$C055	Display page 2
$C056	Lo-Res mode
$C057	Hi-Res mode
$C000	Read keyboard (bit 7 = key ready)
$C010	Clear keyboard strobe

; Switch to Hi-Res page 1, full screen
STA $C057       ; Hi-Res
STA $C050       ; Graphics
STA $C052       ; Full screen
STA $C054       ; Page 1

Keyboard

The Apple II keyboard is polled, not interrupt-driven:

wait_key:
    LDA $C000       ; Read keyboard — bit 7 set when key is ready
    BPL wait_key    ; Loop until bit 7 is set
    AND #$7F        ; Mask off the strobe bit (key is ASCII + $80)
    STA $C010       ; Clear keyboard strobe
    ; A now contains the ASCII key code

Speaker

The Apple II speaker is toggled by reading or writing $C030. Each access flips the speaker membrane:

; Click the speaker (one flip)
STA $C030

; Simple tone — toggle rapidly in a loop
    LDX #tone_period
tone_loop:
    STA $C030       ; Toggle speaker
    DEX
    BNE tone_loop

Generating music means carefully timed toggles in tight assembly loops — a genuine skill on the Apple II.

Hi-Res graphics

The Apple II Hi-Res screen is at $2000. The layout is non-linear (similar to the ZX Spectrum but with a different pattern):

; Address of pixel row Y (0-191) in Hi-Res page 1:
; Addr = $2000 + (Y & 7)*$0400 + ((Y >> 3) & 7)*$80 + (Y >> 6)*$28

Each byte in HIRES controls 7 pixels (bit 7 is a colour palette selector). Pixels are arranged left-to-right, bits 0–6.

The colour rules: - On an NTSC screen, adjacent "on" pixels produce colour (orange, green, blue, violet) - The exact colour depends on horizontal position (even/odd column) and bit 7 of the byte

Most Apple II graphics programmers use lookup tables for row addresses and shape data rather than calculating from scratch.

AppleSoft BASIC quick reference

]HOME               : REM Clear screen
]PRINT "HELLO"
]GR                 : REM Switch to Lo-Res graphics
]HGR                : REM Switch to Hi-Res graphics
]COLOR= 12          : REM Set Lo-Res colour (0-15)
]PLOT X,Y           : REM Plot Lo-Res block at (X,Y)
]HCOLOR= 3          : REM Set Hi-Res colour (0-7)
]HPLOT X,Y          : REM Plot Hi-Res pixel
]HPLOT TO X2,Y2     : REM Draw line
]CALL -936          : REM Clear screen (via ROM)
]CALL address       : REM Call machine code
]PEEK(addr)         : REM Read memory byte
]POKE addr, val     : REM Write memory byte

AppleSoft BASIC variables follow the same 2-significant-character rule as Commodore BASIC. Integers use % suffix, strings use $.

CC65 C on the Apple II

CC65 provides an apple2 (Apple ][+) and apple2enh (Apple //e) target with platform headers:

#include <apple2.h>
#include <conio.h>
#include <stdio.h>

int main(void) {
    /* Clear screen */
    clrscr();

    /* Print at position */
    gotoxy(10, 5);
    cputs("HELLO FROM CC65!");

    /* Switch to Lo-Res graphics */
    /* Use soft switches via POKE-equivalent */
    *(volatile char*)0xC050 = 0;   /* Graphics on */
    *(volatile char*)0xC056 = 0;   /* Lo-Res */
    *(volatile char*)0xC052 = 0;   /* Full screen */

    return 0;
}

The apple2enh.h header adds //e-specific extras like 80-column text and double hi-res graphics.

Common mistakes

Hi-Res colour fringing — the Apple II's colour system means that a solid block of "on" bits produces alternating colours, not a solid colour. Use established colour byte patterns from reference tables rather than guessing.

Non-linear HIRES layout — like the ZX Spectrum, Hi-Res rows are stored non-linearly. Always use a lookup table.

Speaker timing — generating a clean tone requires very precise loop timing. A loop that does other work will produce a buzzing, uneven sound. Keep speaker-toggle loops tight and pure.

Soft switch read vs write — some soft switches care whether you read or write them; others respond to either. In assembly use STA (write) for most; in situations where you're checking a switch state, LDA (read). The cc65 Apple II headers abstract this for common operations.

40 vs 80 columns — the base Apple II is 40 columns. The Apple //e with an 80-column card supports 80 columns. CC65's conio.h targets 40 columns by default; use apple2enh.h for 80-column support.