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XBee Series 2 OEM RF Modules ‐ ZigBee ‐ v1.x2x [2007.07.019]
2.2.5. Sleep Mode
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Sleep modes allow the RF module to enter states of low-power consumption when not in use. To
enter Sleep Mode, one of the following conditions must be met (in addition to the module having a
non-zero SM parameter value):
• Sleep_RQ (pin 9) is asserted
• The module is idle (no data is transmitted or received) for the time defined by the ST (Time
before Sleep) parameter.
Table 2‐01. Sleep Mode Configurations (Router / End Device Firmware Only)
Transition
Sleep Mode
into Sleep
Setting
Mode
Assert (high)
SM=1
Sleep_RQ (pin 9)
Automatic
transition to
SM=4
sleep mode as
defined by the
ST parameter
The SM command is central to setting Sleep Mode configurations. By default, sleep modes are
disabled (SM=0) and the module remains in Idle/Receive Mode. When in this state, the module is
constantly ready to respond to serial or RF activity.
Zigbee Protocol: Sleep Modes
In the ZigBee protocol, sleep modes are only supported on end devices. See section 4.3, "Sleep
Mode Operation" for more information.
Pin/Host Controlled Sleep
Pin sleep puts the module to sleep and wakes it from sleep according to the state of Sleep_RQ
(pin 9). When Sleep_RQ is asserted (high), the module will finish any transmit or receive
operations, and then enter a low power state. The module will not respond to either serial or RF
activity while in sleep.
To wake a module operating in pin sleep, de-assert Sleep_RQ (pin 9). The module will wake when
Sleep_RQ is de-asserted and is ready to transmit or receive when the CTS line is low. When the
module wakes from pin sleep, it sends a transmission to its parent router or coordinator (called a
poll request) to see if it has buffered any data packets for the end device. The module will continue
to poll its parent for data while it remains awake. If the parent receives an RF data packet destined
for one or more of its end device children, it will transmit the packet to the end device upon receipt
of a poll request. See section 4.3, "Sleep Mode Operation" for more information.
Cyclic Sleep
Cyclic sleep allows modules to wake periodically to check for RF data and sleep when idle. When
the SM parameter is set to 4, the module is configured to sleep for the time specified by the SP
parameter. After the SP time expires, the module will wake and check for RF or serial data. To
check for RF data, the module sends a transmission to its parent router or coordinator (called a
poll request) to see if its parent has any buffered data packets for the end device. If the parent
has data for the module, the module will remain awake to receive the data. Otherwise, the module
will return to sleep. (See section 4.3, "Sleep Mode Operation" for more information.)
If serial or RF data is received, the module will start the ST timer and remain awake until the timer
expires. While the module is awake, it will continue to send poll request messages to its parent to
check for additional data. The ST timer will be restarted anytime serial or RF activity occurs. The
module will resume sleep when the ST timer expires.
When the module wakes from sleep, it asserts On/Sleep (pin 13) to provide a wake indicator to a
host device. If a host device wishes to sleep longer than SP time or to wake only when RF data
arrives, the SN command can be used to prevent On/Sleep from asserting for a multiple of SP
time. For example, if SP = 20 seconds, and SN = 5, the On/Sleep pin will remain de-asserted
(low) for up to 100 seconds.
© 2007 Digi International, Inc.
Transition out of
Characteristics
Sleep Mode (wake)
De-assert (0V) Sleep_RQ
Pin/Host controlled
(pin 9)
Transition occurs after the
RF module wakes
cyclic sleep time interval
after a pre-
elapses. The time interval
determined time
is defined by the SP
interval to detect if RF
(Cyclic Sleep Period)
data is present.
parameter.
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Chapter 2 ‐ RF Module Operation
Related
Power
Commands
Consumption
SM
< 1uA
SM, ST, SP, SN
< 1uA
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