xbee uart data present indicator pin vs on_sleep pin


I am using xbee-868lp modules (80k variant). The xbee will be connected to a microcontroller on a pcb and I want to be able to get the mcu to go into low power mode when there is no data received at the xbee.
I was thinking of configuring the xbee in sync cyclic sleep mode (SM= 8 ) and either:

(a) Use the uart data present indicator pin in order to wake/sleep the mcu. Is that the right way to do so?

(b) Or should I use instead the on/sleep pin? Will this wake up the mcu each time the xbee is awake regardless it received something or not?

Yes option A would appear to be the correct way. But I would suggest verifying this pin 12 does work in that manner before you spin your boards.