In the attached zip file are:
- KiCad files for the ROM Interposer Board
- Arduino code for ROM test
- Teensy code to test interrupt latency
- Python code that can respond to an Output Enable signal
A couple of notes that keep coming up:
Q: Why do you need to emulate a ROM chip anyway?
A: Like most 8-bit computers, the keyboard interface eventually talks directly to the memory bus. In an Apple IIe (and IIc), that is done through a ROM chip.
Q: Why not just replace the keyboard matrix?
A: The final design will not use the original keyboard microcontroller or ROM. Ideally, I want to have an interface for a USB keyboard (and possibly Apple Desktop Bus: ADB.)
Q: The Teensy was only 200 nanoseconds, why not just use that?
A: The Mini-Apple IIe is based on the MEGA-II ASIC from an Apple IIgs. Its timing is tighter and slightly different from the Apple IIe’s MMU. The Teensy is slightly too slow.
Q: What is “Golden Delicious”?
A: Originally, I was naming this project “Golden Delicious.” So, let’s call it a code name. Now, I call it “Mini Apple IIe.” But, the final project has a different name.
- Workbench Wednesday 18: Digilent Analog Discovery Review
- Workbench Wednesday 16: Instrument Basics: Logic Analyzer
- Keyboard ROM (26-pin) Interposer Board: https://github.com/baldengineer/Golden-Delicious/tree/master/kicad%20files/ROM%20Interposer%20board
Bill of Material:
|Pi Pico (RP2040)||Raspberry Pi Foundation||1|
|Analog Discovery 2||Digilent||1|
|Teensy 4.0 from PJRC|