APL1

APL1

A homebrew Apple 1 replica built around the 6502 microprocessor, with a modern microcontroller-based terminal that adds PS/2 keyboard and serial input alongside the original ASCII keyboard interface.

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Table of Contents

• Overview
• Architecture
• Hardware
  • APL1 Board
    • Revision History
• Firmware
  • APL1 Controller
  • APL1 ROM
  • APL1 Terminal
• CAD
• Production
• Schematics
• Libraries
• Bill of Materials
• License

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Overview

The APL1 is a faithful recreation of the 1976 Apple 1 computer, rebuilt as an open-source KiCad project. It preserves the original 6502 + PIA architecture and the classic WozMon firmware experience, while replacing the bulky discrete terminal section of the original with an ATmega1284 microcontroller. The MCU emulates the Apple 1 keyboard and display handshake exactly, but also exposes a PS/2 keyboard port and a serial terminal connection for modern convenience.

Architecture

• CPU: MOS 6502 running at 1 MHz
• RAM: 32KB SRAM (AS6C62256)
• ROM: 8KB EEPROM (28C64) holding WozMon
• PIA: 65C21 — the Apple 1 keyboard/display interface
• Terminal: ATmega1284(P) controller emulating the original terminal handshake
• Input: Original ASCII keyboard header, PS/2 keyboard, and serial (RS-232) input
• Output: Serial terminal output, with composite video reserved for a future revision
• Bus: 16-bit address bus, 8-bit bidirectional data bus, standard 6502 control signals
• Clock: 1 MHz oscillator for the 6502; 28.63636 MHz crystal (8× NTSC colorburst) for the controller

Hardware

This repository contains KiCad 7.0+ PCB designs for the APL1 board.

APL1 Board

Hardware/APL1/

The single board hosting the 6502 CPU, memory, PIA, and the ATmega1284 terminal controller. Provides:

• CPU: 6502 running at 1 MHz
• RAM: 32KB SRAM (AS6C62256)
• ROM: 8KB EEPROM (28C64) preloaded with WozMon
• PIA: 65C21 keyboard/display interface (original Apple 1 footprint)
• Terminal Controller: ATmega1284(P) running APL1 Controller firmware
• Keyboard buffer: 74LS245 octal bus transceiver
• Glue logic: 74LS04, 74LS00, and 74LS138 address decoder
• Serial: MAX232 level shifter with DB-9 (DTE) connector
• Input: Original ASCII keyboard header and PS/2 keyboard connector
• Video: RCA composite video jack (reserved for a future firmware revision)
• Reset: Keyboard reset and clear controls handled by the controller
• Power: 5V DC via barrel jack, with power switch and indicator LED

Revision History

Rev 1.1

• Add 10k pull-down resistor R9 for KBDCLR.
• Change pull-up resistors R1-R4 from 1k to 4.7k.
• Add capacitor C17 for bulk capacitance at power supply.

Rev 1.0

• Initial release.

Firmware

This repository contains firmware for the terminal controller, the system ROM, and the desktop terminal application.

APL1 Controller

Firmware/APL1 Controller/

PlatformIO-based firmware for the ATmega1284(P) terminal controller. Provides:

• Faithful emulation of the Apple 1 keyboard and display handshake (DA / RDAB)
• Original ASCII keyboard pass-through via the 74LS245 buffer
• PS/2 keyboard input with a custom Set-2 ISR decoder mapped to Apple 1 ASCII
• Serial (RS-232) terminal input and output at 115200 8N1
• Control shortcuts for clear screen, reset, and throttle ("slow") mode
• Keyboard reset and clear button handling
• Composite video output hooks reserved for a future revision

See Firmware/APL1 Controller/README.md for build, flash, and pin-map details.

APL1 ROM

Firmware/APL1 ROM/

The system ROM image built from WozMon, Steve Wozniak's original Apple 1 monitor, assembled with the cc65 toolchain and burned to a 28C64 EEPROM.

See Firmware/APL1 ROM/README.md for build and programming instructions.

APL1 Terminal

Firmware/APL1-Terminal/

An Electron + Vue 3 desktop application that provides a faithful CRT terminal experience for the APL1. Connects to the board over the DB-9 serial port at 115200 8N1 and renders output using the original Signetics 2513 character ROM glyphs. Provides:

• 40×24 character canvas rendered with the authentic Signetics 2513 font
• Selectable phosphor color: white, amber, or green
• CRT effects: phosphor glow, scanlines overlay, and screen flicker animation
• Serial port connection and disconnection (auto-detected ports)
• Keyboard input forwarded to the APL1 with Apple 1 control shortcuts (Ctrl+L clear, Ctrl+\ reset, Ctrl+T throttle)
• Built-in program loader with paced character/line sending for 20 bundled Wozmon programs
• Settings panel with per-character and per-line delay controls
• macOS (Apple Silicon DMG), Linux (AppImage / deb), and Windows (NSIS installer) distribution builds, all built locally from macOS

See Firmware/APL1-Terminal/README.md for build and run instructions.

CAD

CAD/

3D models and images for the APL1 board and its components.

Production

Production/

JLCPCB-ready fabrication files, BOM, and component positions for PCB fabrication and assembly.

Schematics

Schematics/

Schematics for the APL1 board.

Libraries

Libraries/

Shared KiCad symbol and footprint libraries used across the APL1 hardware project.

Bill of Materials

License

Hardware designs are released under the CERN Open Hardware Licence Version 2 – Permissive.