Managing End Devices XBee End Device configuration
XBee/XBee-PRO ZigBee RF Modules User Guide 91
timeout mechanism in order to allow enough time for the end device to wake and receive the data transmission
from its parent.
If a non-parent device does not know the destination is an end device, it will use the standard unicast timeout for
the transmission. However, provisions exist in the Ember ZigBee stack for the parent to inform the message
sender that the destination is an end device. Once the sender discovers the destination device is an end device,
future transmissions will use the extended timeout. See XBee ZB Router/Coordinator configuration on page 98
for details.
XBee End Device configuration
XBee end devices support two different sleep modes:
Pin Sleep
Cyclic Sleep.
Pin sleep allows an external microcontroller to determine when the XBee should sleep and when it should wake
by controlling the Sleep_RQ pin. In contrast, cyclic sleep allows the sleep period and wake times to be configured
through the use of AT commands. The sleep mode is configurable with the SM command.
In both pin and cyclic sleep modes, XBee end devices poll their parent every 100ms while they are awake to
retrieve buffered data. When a poll request has been sent, the end device enables the receiver until an
acknowledgment is received from the parent. (It generally takes less than 10ms from the time the poll request is
sent until the acknowledgment is received.) The acknowledgment indicates if the parent has buffered data for
the end device child or not. If the acknowledgment indicates the parent has pending data, the end device will
leave the receiver on to receive the data. Otherwise, the end device will turn off the receiver and enter idle mode
(until the next poll request is sent) to reduce current consumption (and improve battery life).
Once the module enters sleep mode, the On/Sleep pin (pin 13) is de-asserted (low) to indicate the module is
entering sleep mode. If CTS hardware flow control is enabled (D7 command), the CTS pin (pin 12) is de-asserted
(high) when entering sleep to indicate that serial data should not be sent to the module. The module will not
respond to serial or RF data when it is sleeping. Applications that must communicate serially to sleeping end
devices are encouraged to observe CTS flow control.
When the XBee wakes from sleep, the On/Sleep pin is asserted (high), and if flow control is enabled, the CTS pin is
also asserted (low). If the module has not joined a network, it will scan all SC channels after waking to try and find
a valid network to join.
Pin sleep
Pin sleep allows the module to sleep and wake according to the state of the Sleep_RQ pin (pin 9). Pin sleep mode
is enabled by setting the SM command to 1.
When Sleep_RQ is asserted (high), the module will finish any transmit or receive operations and enter a low
power state. For example, if the module has not joined a network and Sleep_RQ is asserted (high), the module
will sleep once the current join attempt completes (i.e. when scanning for a valid network completes). The
module will wake from pin sleep when the Sleep_RQ pin is de-asserted (low).
To Next Page
Loading...
Need help?
General
