LisaList2

The first prototype Macintosh computers had a 5.25" Twiggy Drive instead of the 3.5" Sony drive used in production models.

The Mac Twiggy Drive is the same as the Lisa Twiggy drive, aside from the Digital Board which is the subject of this topic.

All the pictures I have are at:

https://www.flickr.com/photos/114907644@N04/albums/72177720300046948

Schematic, Parts List, Dimensions (in inches), PAL equations, Notes

For compatibility with PALASM 4, the PAL equations indicate the target is a PALCE16V8, which is functionally equivalent to a GAL16V8, so the JEDEC fuse map can be used for both parts.

The Notes were thoughts about changes that one might make if making more of these boards.

NB: I have not made a board from these documents -- there may be omissions or errors. Feel free to ask questions.

The GAL was tested (and is in two Twiggy Macs replacing the original but damaged 16L8 parts).

Errata..

in Dimensions.pdf: The Y coordinate of J1 appears to have been measured from the bottom (instead of the top of the drawing as indicated)

in Schematic.pdf: the PAL/GAL U5 is not shown. Connections to U5 are designated in areas of the circuit by pin number, eg. U5-10 is pin 10 of the PAL. This is an artifact of having made the schematic in order to determine PAL equations, so the schematic was in fact "drawn around" the PAL.