To be fair, I cannot say with certainty why it works; I don't have code for the BIOS or EC. The CoreBoot and LibreBoot people might be able to shed some light.
The more interesting aspect, verified by testing, is that it does work.
In my own testing, SCL to SDA will not work on the T2X, T3X, T4X, T60, X2X, X3X, X4X, or X60. It does work on the T61/X61 and T400/500.
PROT to GND works on all of the above. I also tested it on an X230 (works), but I didn't check SCL to SDA on that machine.
thanks for the list of combinations of Thinkpad models regarding SCL/SDA and PROT/GND. I tried SCL/SDA on my T60, of course it did not work... Do you happen to know how to locate PROT and GND on the top of T60 mainboard? Unfortunately the guide on ja.axxs shows only where SCL and SDA is located. Really appreciate it, thanks!
GND and PROT are pins 31 and 32 on the same chip, right next to SCL and SDA on the 8356908. I don't know where PROT might be exposed on the top of the PCB, it very well might not be. I soldered leads directly to the chip to test.
The more interesting aspect, verified by testing, is that it does work.
In my own testing, SCL to SDA will not work on the T2X, T3X, T4X, T60, X2X, X3X, X4X, or X60. It does work on the T61/X61 and T400/500.
PROT to GND works on all of the above. I also tested it on an X230 (works), but I didn't check SCL to SDA on that machine.