The Apple RTC has finally been reverse engineered!

[Kai Robinson]

Please note - all credit goes to Phil Greenland for this:

New Timepiece for a Classic Mac – Part 1

Restoring a Macintosh SE/30: replacing its leaky lithium‑battery RTC with a microcontroller‑based emulator, detailed circuit analysis and repair steps.

www.quantulum.co.uk

New Timepiece for a Classic Mac – Part 2

Continuation of the project to replace the aging RTC module in a Classic Macintosh SE/30—now using the ATTiny85 USI interface, PCB design and pin‑compatible module details.

www.quantulum.co.uk

So for anyone with a classic mac needing the 8-pin DIP package RTC, this is the answer!

I have an idea that this might be possible to implement in a 20-pin PLCC footprint...

 

[trag]

Thank you for that, @Kai Robinson

While reading Part 1 I kept wondering why the author and his predecessor didn't use the Serial pins on the ATTiny.

Heh, then I read Part 2.