XBee®/XBee‐PRO® ZB SMT RF Modules
DIN
ST = Time Awake
On/Sleep
A cyclic sleep end device enters sleep mode when no serial or RF data is received for ST time .
Legend
On/Sleep
Transmitting Poll
Request
Sleep Period
The sleep period is configured based on the SP, SN, and SO commands. The following table lists the
behavior of these commands.
Command
Range
Description
0x20 - 0xAF0 (x 10 ms)
(320 - 28,000 ms)
SP
Configures the sleep period of the module.
Configures the number of sleep periods
multiplier.
SN
1 - 0xFFFF
Defines options for sleep mode behavior.
0x02 - Always wake for full ST time
0x04 - Enable extended sleep (sleep for full
(SP * SN) time)
SO
0 - 0xFF
The XBee module supports both a short cyclic sleep and an extended cyclic sleep that make use of these
commands. These two modes allow the sleep period to be configured according to the application
requirements.
Short Cyclic Sleep
In short cyclic sleep mode, the sleep behavior of the module is defined by the SP and SN commands, and
the SO command must be set to 0x00 (default) or 0x02. In short cyclic sleep mode, the SP command
defines the sleep period and is settable up to 28 seconds. When the XBee enters short cyclic sleep, it
remains in a low power state until the SP time has expired.
After the sleep period expires, the XBee sends a poll request transmission to its parent to determine if its
parent has any buffered data waiting for the end device. Since router and coordinator devices can buffer
data for end device children up to 30 seconds, the SP range (up to 28 seconds) allows the end device to poll
regularly enough to receive buffered data. If the parent has data for the end device, the end device will
start its sleep timer (ST) and continue polling every 100ms to receive data. If the end device wakes and
finds that its parent has no data for it, the end device can return to sleep immediately.
The SN command can be used to control when the On/Sleep line is asserted (high). If SN is set to 1
(default), the On/Sleep line will be set high each time the XBee wakes from sleep. Otherwise, if SN is
greater than 1, the On/Sleep line will only be set high if RF data is received, or after SN wake cycles occur.
This allows an external device to remain powered off until RF data is received, or until a number of sleep
periods have expired (SN sleep periods). This mechanism allows the XBee to wake at regular intervals to
poll its parent for data without waking an external device for an extended time (SP * SN time). This is
shown in the figure below.
© 2010 Digi International, Inc.
85
DCD [ DIGITAL CORE DESIGN ]
