The Apple IIe’s IOU (Input/Output Unit) and MMU (Memory Management Unit) are two custom integrated circuits (ICs) that played a crucial role in the computer’s design. Developed by Apple in the early 1980s, these chips consolidated much of the system’s complex circuitry into single components. However, once Apple ceased production of the Apple IIe, the manufacture of these chips also stopped. For decades, the only way to replace a faulty IOU or MMU has been to scavenge them from other Apple IIe units—a diminishing resource.
This project offers a modern solution: a VHDL-based reimplementation of the Apple IIe's IOU and MMU, faithfully based on original Apple schematics. The goal is to preserve the technology behind these essential ICs and provide the means to create replacement adapters, ensuring that damaged chips no longer spell the end for an Apple IIe.
This project is code-only and does not include any hardware designs such as Gerber files or a Bill of Materials (BOM) for building physical adapters. If you're looking to integrate this into an Apple IIe, you'll need to design your own hardware or find third-party solutions that suit your needs.
On the other hand, ReActiveMicro is currently designing and manufacturing a replacement adapter based on this project, and should be available relatively soon.
The IOU and MMU has been thoroughly tested and is functionnal.
The implementation has been tested with these hardware components:
- Motherboards:
- Rev.B motherboard
- ReActiveMicro motherboard
- CPU:
- Synertek 6502 (unenhanced ROMs)
- Rockwell 6502 (unenhanced ROMs)
- 65C02 (enhanced ROMs)
- AUX Cards:
- RAMWORKS III aux card
- 80-Col Expansion card (820-0067-B)
- 80-Col Expansion card (820-0067-D)
- ROMs:
- Enhanced ROMS from ReActiveMicro
- Unhanced ROMS (342-0132-B, 342-0133-A, 342-0134-A, 342-0135-A)
- Disk Interfaces
- Apple 5.25 Drive Controller Card (655-0101-E)
- Disk ][ Interface Card (650-X104)
- Other
- Mouse Interface 670-0030-C
- COMMON: Components common to the MMU and the IOU.
- CUSTOM: Components that may need to be changed depending on the hardware used.
- TTL: Implementation of a few TTL components used in the schematics.
- MMU: Components that makes the MMU.
- IOU: Components that makes the IOU.
- Documentation: Help on understanding the IOU and MMU, and help on implementing hardware replacement adapters.
- test: Testing components, testbenches and test-cases; has the same structure as the base directory.
This repository is licensed under the Creative Commons Zero License. You are free to use, modify, distribute, and build upon the code in any way you see fit. The Creative Commons License grants you the freedom to adapt the code for personal, academic, commercial, or any other purposes without seeking explicit permission.