Supercon 2023: James Lewis Builds His Own Portable Apple IIe

This talk spans a four-year project initially intended to be a quick and easy “just wire this chip up” idea. (Sound familiar?) James set out to build a portable Apple IIe based on the Apple “Mega-II” chip from the late 1980s. Something that not even Apple ever did! To make it happen, he had to reverse engineer the (mostly) undocumented ASIC and learn more about the Apple II hardware architecture than a single person should.
The result is the first Apple IIe-compatible computer built relying on the Mega-II - not even the IIGS can claim this!
Read the story on Hackaday:
hackaday.com/2...

[@higaski]

What a journey, great talk

[@bald_engineer]

Thanks!

[@SojournerDidimus]

26:20 I remember one of the Apple II machines had this "clever" trick with a Green/Magenta screen, where is could either drive both the green and the magenta subpixels, *or* the green from one and the magenta from the adjacent pixel! They used this to double the solubility (not the resolution) of the screen. Like a predecessor to modern anti-aliasing.
Might it be that the Mega II has a similar trick, where it "knows" the arrangement of the subpixels and shifts them over per subpixel instead of per pixel to add to the apparent resolution? You could try outputting to a genuine IIe display to see if it "works".

[@bald_engineer]

The IIGS's composite circuit, which I used for the early stages of the project, doesn't output the same composite signal as the IIe. Mega's 4-bit RGB signals and SERVID (the luma/chroma data for each line) output the same data. The 4-bit RGB signals are a de-muxed copy of SERVID. Unfortuantely, SERVID does not behave exactly like the SERVID on the II+/IIe.