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Overview of the Apple II system

A partial implementation of an Apple II Plus.

Core library: Highbyte.DotNet6502.Systems.Apple2.

CPU: the NMOS 6502 model (nmos6502) by default, as in the Apple II/II+/unenhanced IIe. The NCR 65C02 model (ncr65c02) can be selected in the system configuration.

The currently supported system variant is APPLE2PLUS.

Current capabilities

  • Run Applesoft BASIC and the Autostart Monitor from user-supplied Apple II Plus ROMs.
  • 48 KB base RAM and an optional 16 KB language card, enabled by default. The resulting 64 KB configuration supports ProDOS 8. See Language card.
  • 12 KB system ROM. Both 12 KB ROM images and the common 20 KB image layout are accepted.
  • Apple II text and graphics:
    • 40 × 24 text with normal, inverse, and flashing characters.
    • 40 × 48 lo-res graphics.
    • 280 × 192 hi-res graphics with NTSC artifact colours.
    • Mixed graphics and text modes.
    • Composite colour, green, white, and amber monitor options.
  • Two video render providers:
    • Rasterizer (default) renders text, lo-res, and hi-res graphics from the character ROM.
    • VideoCommands is a lightweight text-only fallback for character-cell hosts.
  • Read-only Disk II controller in slot 6. It boots standard 16-sector images in DOS 3.3 or ProDOS sector order, detected automatically. See Disk II.
  • Apple II game-port support for paddles and two buttons. A host gamepad works directly; optional keyboard joystick controls use W/A/S/D, Space, and Left Shift.
  • Host keyboard input with Shift, Control, and key repeat. US English and Swedish layouts are supported, with automatic host-layout detection or an explicit setting.
  • Built-in speaker audio, including software-generated effects and sampled audio.
  • CTRL-RESET using Ctrl + F12.
  • Program loading in the Avalonia apps:
    • Tokenized Applesoft BASIC files and DOS 3.3 binary files.
    • Applesoft and binary programs loaded directly from DOS 3.3 disk images.
    • Bundled BASIC and assembly examples.
    • Curated downloadable programs and bootable games.
  • Copy and paste of Applesoft BASIC source in the Avalonia sidebar.
  • Remote-control commands for keyboard input, BASIC source, and Disk II operations. See the TCP protocol.
  • Avalonia Desktop and Avalonia Browser (WASM) apps with configuration for ROMs, display, audio, input, and CPU compatibility, plus text-mode support in the Terminal (TUI) app.
  • Emulator state snapshots, including the language card and inserted disk. See Snapshots.

Disk II support

The Disk II controller can insert and boot standard 16-sector .dsk and .do images. DOS 3.3 and ProDOS sector ordering are both supported and detected from the image contents. ProDOS 8 runs when the language card is enabled.

The Avalonia apps can also use a DOS 3.3 disk image as a file source, loading an Applesoft or binary program directly into RAM without booting the disk.

The drive is read-only and supports one drive. Disk writing and nibble/flux image formats are not implemented. See Disk II for details.

Language card

The optional language card adds 16 KB of bank-switched RAM over the system ROM address space, bringing the machine to 64 KB. It is enabled by default and can be disabled in the configuration dialog to emulate a plain 48 KB Apple II Plus.

The card allows ProDOS 8 to run and is also used by DOS 3.3 software. Its memory and switch state are included in emulator snapshots.

Snapshots

Apple II .d6502snap snapshots save the CPU, base RAM, language card, display state, keyboard, speaker, game port, Disk II controller, and inserted disk. Audio, keyboard-joystick, and monitor settings can be included as portable settings.

ROMs are not stored in a snapshot; they are loaded from the destination system's configuration when the snapshot is restored.

Monitor commands

Additional machine code monitor commands specific to the Apple II system:

Commands:
  lb     Apple II - Load a tokenized Applesoft BASIC file (no header) from file picker dialog.
  llb    Apple II - Load a tokenized Applesoft BASIC file (no header) from host file system.
  sb     Apple II - Save a tokenized Applesoft BASIC file (no header) to host file system.

For general monitor commands, see Monitor library.

Not yet implemented

  • Fully NTSC-accurate hi-res artifact colour.
  • Disk II writing, a second drive, and nibble/flux disk images.
  • Sound cards such as the Mockingboard.
  • Peripheral slots other than slot 6, cassette, and the second paddle pair.
  • Other Apple II family models, including the original Integer BASIC Apple II and Apple IIgs.

ROMs

See ROMs.