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

You are definatly ambitious in trying to reverse engineer the old Apple II.

I never played with one of those, we went with CPM Z80 machines, but I am familiar with the issues with the dynamic ram access of that era.

I found your debug sequence very interesting and you brought back memories of doing similar work back in those days.

Good luck with your build, it will be interesting to see what hidden capability resides in that chip.

DAB

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!

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!

Hope this helps

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."