I'd like to point a couple of things:

1) bbraun, another BIG THANK YOU for your effort making these small but very interesting pieces of code. They're very helpful, even without reaching total success.

2) I'm... errr... an idiot :I The via (inter-layer connection, not the 6522 VIA) I was probing in these tests (marked P on the first picture of this thread) is not connected to VIA2-PB2 as I supposed xx(

Anyway, with the SE/30 in service mode, I did some more tests probing the actual VIA's pin. In short, results are:

1. Your Power Off application does toggle PB2, as expected -- no hardware surprises here
   
2. The Finder's Shutdown command does not toggle PB2 -- no matter if your Sysv hack is installed or not
   
3. Pin 81 (C1) on the PDS socket keeps at +5 V forever, even if PB2 has toggled by your app.

[Aaaargh! Hit the send button too early...]

But an interesting result came out from your Power Off app... the Data Direction Register 2, before any action, was set as 0x80, thus leaving PB2 as a high-impedance input, staying at "1" thanks to the pull-up. It could be that the soft-power capabilities are decided very early in the start-up sequence, via Gestalt before any extension could change it and, if not present, PB2 gets configured as an input. That way, the Finder won't bother with the availability of soft-power upon issuing the Shutdown command: it just "toggles" PB2 which, if set as an input, won't come out. Makes sense to me.

Maybe all that is needed to enable PB2 control is to set it as an output in the Data Direction Register? (shameless plug) :I I really should dust off Codewarrior and try it by myself...

Thanks again,