Apple II Emulation on an AVR Microcontroller

The Apple ][ personal computer was one of the first three completely assembled systems on the market. It was sold several million times from April 1977 till 1993. This 8 bit home computer was developed by Steve »The Woz« Wozniak and evolved together with Steve Jobs. They paved the way for the Apple Macintosh computer and the nowadays well known brand Apple with its products. Back in 2014 I wrote my Bachelor thesis about emulating a complete Apple ][ (»two«) on an Atmel AVR microcontroller. The thesis describes the implementation of a software emulator for the complete Apple ][ computer system on a single Atmel AVR microcontroller unit (MCU). Although the microcontroller runs at 20 MHz and the Apple ][ runs at roughly 1 MHz it is quite a challenge to get this working. The microcontroller not only emulates the original processor of the Apple ][ computer - the famous MOS 6502 - but also performs other tasks like display output and keyboard input. This requires an efficient emulation of the 6502 and memory management since the resources of a microcontroller are very limited when intending such challenging operations. The thesis shows the development of the processor emulation software and examines different design patterns of reaching the goal of a fast processor emulation. For every different approach the strenghts and weaknesses are scientifically evaluated. The final product is a highly improved emulation of the MOS 6502 CPU, written in AVR assembler, which is then used on an AVR ATMega 1284p microcontroller together with other electronic parts to create a portable and battery powered Apple ][ (emu­lator) handheld prototype.”


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