This project started as a portable Apple ][ by using the Mega-II chip from an IIGS. (This chip is precursor, and slightly different to the Gemini in the Mac LC compatibility card.) However, it evolved into making a miniture Apple IIe compatible computer.
This repo contains the KiCad design files, RP2040 firmware, and notes for the Mega IIe computer.
This element14 Presents video documents the effort to get from an Applesoft Prompt to a fully functional computer, in a miniature case.
https://www.youtube.com/watch?v=gFCD4s_hsb4
You can find additional information on the element14 Community or in this Hackster.io article.
This project is why I started Bit Preserve, a project to archive vintage computer schematics.
When live streaming the probject, I kept some notes here for future reference.
- Attempting to book the GD with a IIc ROM results in a lock-up.
- graphics get initialized and the memory is dumped to the screen, but no beep and nothing past that.
- Logic Analyzer suggests
BASICINITis doing a monitor version check in the F8 ROM, but failing. It calls a jump calledHANG. Even though the 6502 should be jumping in a circle, it seems to keep doing other stuff. (Maybe it is just bus fetches that do nothing?)
- SLOTMAKER Bus Headers on the IO board are pinned out different from the SLOTMAKER Bus Header on the MEGA-65c02. For a ribbon cable, each pin-pair needs to be swapped, except for the last two. They are GND.
Golden Delicious Rev 2 booted! Yay!
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~DMA is wrong level
- The two `245 buffers have their enable pins connnected to ~DMA. I made the mistake of thinking that MEGA drove the ~DMA signal. That is not the case, nor does it make sense after thinking about it. For now, the `245s have pin 19 lifted and tied to ground to always enable them.
- When connecting the IWM or a card to slotmaker, ~DMA situation needs to be resolved.
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IIe / 6502 decoder for Waveforms / Digitial Discovery has been updated.
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This forum post has Digilent Waveforms beta builds that are downloadable without filling out the annoying registration form. (Or just use
asdffor all of the fields.)
- Wherefore no IIe ROM in the IIgs? Is it in the MEGA-II?
- Warphammer: this seciton looks rommy
- rjhelms: that's the big question mark - there could be logic in the Mega II that never actually gets used because the CYA is doing it all in this implementation
- al: keep it all breakouts
- can we decode ROMEN1 and ROMEN2 ourselves?
Things to look at on the scope:
- Composite signal out of the Mega II
- What is Mono-Color from VGC doing to Chroma into MC1377
- Is VGC refreshing apple II DRAM (or is it the Mega)
- why is the 28 MHz oscillator enabled/disabled from the VGC's !SYNC pin?
- PLCC Pinout Page
- XL H 7 3 5 0 28.636360 I
- XL = 1,000,000 af
- H = LVCMOS En/Dis Pin 1
- 7 = 7.0 x 5.0 mm
- 3 = 3.3 VDC
- 5 = 100ppm for -40C to 105C only on tuesdays when the moon is full and it hasn't rained for a few days. also if you ate green skittles recently Note1
