User's Manual

XBee®/XBee‐PRO®ZBRFModules
©2009DigiInternational,Inc. 81
Note: SP controls the packet buffer time on routers and coordinators. SP should be set on all
router and coordinator devices to match the longest end device SP time. See the XBee Router /
Coordinator Configuration section for details.
Extended Cyclic Sleep
In extended cyclic sleep operation, an end device can sleep for a multiple of SP time which can
extend the sleep time up to several days. The sleep period is configured using the SP and SN
commands. The total sleep period is equal to (SP * SN) where SP is measured in 10ms units. The
SO command must be set correctly to enable extended sleep.
Since routers and coordinators can only buffer incoming RF data for their end device children for
up to 30 seconds, if an end device sleeps longer than 30 seconds, devices in the network need
some indication when an end device is awake before they can send data to it. End devices that use
extended cyclic sleep should send a transmission (such as an IO sample) when they wake to
inform other devices that they are awake and can receive data. It is recommended that extended
sleep end devices set SO to wake for the full ST time in order to provide other devices with enough
time to send messages to the end device.
Similar to short cyclic sleep, end devices running in this mode will return to sleep when the sleep
timer expires, or when the SI command is received.
Transmitting RF Data
An end device may transmit data when it wakes from sleep and has joined a network. End devices
transmit directly to their parent and then wait for an acknowledgment to be received. The parent
will perform any required address and route discoveries to help ensure the packet reaches the
intended destination before reporting the transmission status to the end device.
Receiving RF Data
After waking from sleep, an end device sends a poll request to its parent to determine if the parent
has any buffered data for it. In pin sleep mode, the end device polls every 100ms while the
Sleep_RQ pin is de-asserted (low). In cyclic sleep mode, the end device will only poll once before
returning to sleep unless the sleep timer (ST) is started (serial or RF data is received). If the sleep
timer is started, the end device will continue to poll every 100ms until the sleep timer expires.
On/Sleep
Δt = SP
Δt = SP * SN
(SN = 1)
Setting SN > 1 allows the XBee to silently poll for data without asserting On /Sleep. If RF data is received
when polling, On/Sleep will immediately assert .
Transmitting poll request to parent
Δt = SP
Sleep_RQ
Transmitting Poll
Request
Legend
Δt = SP * SN
On/Sleep
(SN = 3)
Transmitting poll request to parent