PCNC1100 or 770 Enclosure Door Switch

How does PathPilot learn about the enclosure door switch kit?
I dont see any signal on the DB25 that could be used for such signaling.
Yet there is an indicator on the status page that will show that state.
What am I missing?

The X, Y, and Z limit switches without the door switch installed are all on separate signal lines. With the door switch installed the X and Y axes are combined onto one line and the door switch uses the line that was freed up.