Inside of the Apple IIgs computer is a chip called the MEGA-II. Many sources call this an “Apple IIe on a chip.” Turns out, that might be a bit of a stretch. For this build, James shows how he removed the chip from a 1990-vintage Apple IIgs and put it into a custom-designed prototype. Spoiler: It takes more than 1 chip to make a bootable Apple IIe clone, using a combination of original vintage and modern parts.
Supplemental Content:
- Episode 517: Emulate an EPROM - How Hard Could it Be?
- Workbench Wednesday 18: Digilent Analog Discovery Review
- Bit Preserve (Vintage Computer Schematics in KiCad): https://github.com/baldengineer/bit-preserve
- OSH Park (PCB Fab)
- Golden Delicious Design Files: https://github.com/baldengineer/Golden-Delicious
- Apple IIe ROM Decoder for Digilent Waveforms: https://github.com/baldengineer/Golden-Delicious/tree/master/waveforms%20decoders
- Live Stream List:
- Parts 1, 2, and 4 are lost forever! (well, from Twitch)
- Part 3: Portable Apple II HW Design in KiCad (Aborted Breakout board)
- Part 5: VGC Prototype PCB Design
- Part 6: W65c02 Prototype PCB Design
- Part 7: MEGA-][ Prototype PCB
- Part 8: Measuring ASICs on the Apple IIe
- Part 9: Continued MEGA-][ Design
- Part 10: Creating the 65c02 proto-pcb
- Part 11: First look at emulating Keyboard ROM
- Part 12: Attempting to use an Arduino Mega 2560 to emulate the keyboard ROM. (We failed and the logic analyzer shows why.)
- Part 13: Learning how to program the Pi Pico PIO, so we can use it to emulate the Keyboard ROM
- Part 14 Connecting the Pi PIco to a real Apple IIe
- Part 15: Soldering the analog section of the Video Prototype board
- Part 16: Video and VGC oscilloscope measurements on a working IIgs
- Part 17: Soldering 65C02 Prototype board (and partial test)
- Part 18: Soldering MEGA-II Prototype board (but no testing)
- Part 19: Removing the MEGA, DRAMs, DAC Resistor Packs, and Inductors from a working IIgs. (And then testing the clock dividers on the MEGA!)
- Part 20: Finish soldering the VGC Rev 1 Board.
- Part 21:Last solder focused stream for the rev 1 boards....
- Part 22: Early Turn-On. (Lots of logic analyzer work in this one.)
- Part 23: Verifying the MEGA-II refreshes the DRAM.
- Part 24: Major Milestone: We booted the Apple IIe ROM!!!! (kinda)
- Part 25: Debugging the non-booting (with working video)
- Part 26:This was it! The first boot Passed self-test and got to an Apple prompt (then crashed.)
- Part 27: Attempting to get the Pi Pico PIO to make the databus happy.
- Short Clips
Bill of Material:
| Product Name | Manufacturer | Quantity | Buy Kit |
|---|---|---|---|
| Tablet Oscilloscope | Multicomp Pro | 1 | Buy Now |
| Digital Discovery | Digilent | 1 | Buy Now |
| Analog Discovery 2 | Digilent | 1 | Buy Now |
| Surface Mount Test Points | Harwin | 1 | Buy Now |
| 40 Pin Socket | Multicomp Pro | 1 | Buy Now |
| 100 ohm resistor network | Panasonic | 1 | Buy Now |
| Octal Bus Transceiver (HCT245) | Nexperia | 1 | Buy Now |
Additional Parts:
| MEGA-][ ASIC from Apple IIgs |
| VGC ASIC from Apple IIgs |
| W65c02 from Western Design Center (WDC) |
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