Alain, surely that was obvious ....... Nah, must admit that it wasn't all that clear in the datasheet.

I figure the PIR must be driving the output with resistors since there would otherwise often be a collision when the MCU drives the pin. No good. Driving via resistors will always be sensitive to capacitance on the lead and therefore a settlingtime will be needed. I figured it had to be this way since they specified tbit as "Data bit settling time" with a 10pF load.