XBee®/XBee‐PRO® ZB SMT RF Modules
On/Sleep
(SN = 3)
On/Sleep
(SN = 1)
Δt = SP * SN
Δt = SP * SN
Transmitting poll request to parent
Transmitting poll request to parent
Δt = SP
Δt = SP
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 .
Legend
Sleep_RQ
Transmitting Poll
Request
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.
© 2010 Digi International, Inc.
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DCD [ DIGITAL CORE DESIGN ]
