World’s First Single-Chip Apple II Boots! -- Episode 532

I have no i dea whow you managed to pull this stunt of. amazing!

Thank you Max! Always glad to see you.

I have schematics for all of the IIgs revisions and one for the IIe expansion card. In fact, I re-drew the IIgs schematic in KiCad.

What I'm missing is a functional description of what the Mega-II does. Most of the pins that exist in the IIe's MMU and IOU chipset are straightforward.

But, it is not clear about signals that don't exist in the older chips OR some of the control signals that have glue logic in the older design. For example, I don't know if the DMA signal that Mega has gates the system clock or not. (I have a way to test, but I haven't yet.)

I keep joking I'm going to make a faux-datasheet when I'm "done."

Hope this helps

So awesome! Excited to follow this project as it progresses. :) 

Back in my storied past I did some design work for a 2901.

We had to design a 16 bit computer using them for my class on advanced computer architecture.

Ironically, the professor I had worked for the same company when I was doing computer architecture analysis on an integrated avionics box to combine communications, navigation and identification waveforms a few years later. The project was a very early implementation of what we call SDR today. 

/members/baldengineer this happened while I was at Interdata we used AMD 2901 slices for our CPUs. So I blocked out the CPU which would use 2 of the 2901s so I said what the hell I'll just use 2 more and end up with a 16-bit machine. 

I'm not sure if I'll ever build a custom 8-bit computer. But if I did, I would probably do a Z80 just to expand my knowledge.

6502 is great. But I'm ready to learn a new microprocessor.

Another title I considered for the video was: "how I accidentally reverse engineered the Apple II." I've had to really learn the hardware design of the original Apple II to understand what the Mega-II is doing (and why).

The Rev 2 of the project is pretty far along. One of the most interesting finds is that the supposed "single chip Apple II" needs at least one other ASIC from the IIgs to be functional.It is the chip that buffers the clock signals for the expansion slots. For SOME reason, it has a keyboard-related signal on it. Without that signal it is extremely difficult to get keyboard calls to work correctly. Maybe that'll be in Part 2.

It's clear to me the objective of the chip changed during design phase. I just WISH I could get an internal datasheet for it!

Thanks Mike. The project has been a blast. I really did think I could "just" take the Mega-II out of an IIgs and put it into a custom board. Easy weekend project.

4 years later. (Although, I've only gotten serious about working on the project in the past year.)

The current Rev 2 system is way more functional. It actually boots (and plays) Oregon Trail now! (With some issues.)