Yes, I suppose "General Purpose IO line pass" is what I'm asking about, but the question is . . . what AT command turns it on/off, and what associates which Dn on the input to a Dn on the output? Or . . . is it always on in 802.15.4 devices and always same=same on which Dn is mapped to which Dn? There are examples here http://www.digi.com/blog/videos/xbee-tech-tip-digital-io-line-passing-with-xbee/ and here http://examples.digi.com/sensors/802-15-4-digital-input-with-a-button/ But neither of them (or anywhere else I can find) explain what triggers the association from side to side. Or . . . is it just always on?