Sleep modes
Putting XBee modules into a temporary sleep state preserves battery life when using wireless networks. DigiMesh modules support five sleep modes that are classified as synchronous or asynchronous.
Note Asynchronous sleep modes should not be used in a synchronous sleeping network, and vice versa.
Synchronous sleep modes
Synchronous modes allow all XBee modules to sleep and wake at the same time.
An XBee module in synchronous sleep support mode synchronizes with a sleeping network, but does not sleep. At any time, a sleep support node responds to new nodes that are attempting to join the sleeping network with a sync message. It only transmits normal data when the other nodes in the sleeping network are awake. Sleep support nodes are especially useful as preferred sleep coordinator nodes and as aids in adding new nodes to a sleeping network. To enable synchronous sleep support, set the Sleep Mode (SM) parameter to Sleep Support [7].
An XBee module in synchronous cyclic sleep mode sleeps for a programmed time, wakes in unison with other nodes, exchanges data and sync messages, and then returns to sleep. While asleep, it cannot receive wireless or serial data. To enable synchronous sleep support, set the Sleep Mode (SM) parameter to Synchronized Cyclic Sleep [8].
Asynchronous sleep modes
Asynchronous modes allow you to control the sleep state of a single XBee module.
Pin sleep allows an external microcontroller to determine when the XBee module should sleep and when it should wake by controlling the Sleep_RQ pin (pin 9). When Sleep_RQ is asserted (high) by connecting it to 3.3 volts, the XBee module finishes any operation and enters a low power state. The XBee module wakes when the Sleep_RQ pin is de-asserted (low).
Cyclic sleep allows the XBee module to sleep for a specified time (SP) and wake for a short time (ST) before returning to sleep again. If the XBee module receives serial or wireless data while awake, it extends the time before it returns to sleep by the amount specified by the ST parameter. Otherwise, it enters sleep mode immediately. Parameters SO, SN, SP and ST control the sleep cycle.
The cyclic sleep with pin wake-up is a slight variation of the cyclic sleep mode that allows the XBee module to be woken prematurely by de-asserting the Sleep_RQ pin. The XBee module does not sleep when the Sleep_RQ is de-asserted. Parameters SO, SN, SP and ST control the sleep cycle.