Non-Parent Device Operation; End Device Configuration - Digi XBee-PRO S2C Zigbee User Manual

Manage End Devices

Non-Parent device operation

Devices in the Zigbee network treat data transmissions to end devices differently than transmissions
to other routers and coordinators. When a device sends a unicast transmission, if it does not receive a
network acknowledgment within a timeout, the device resends the transmission. When transmitting
data to remote coordinator or router devices, the transmission timeout is relatively short since these
devices are powered and responsive.
However, since end devices may sleep for some time, unicast transmissions to end devices use an
extended 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 uses 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. For more
information see Router/Coordinator

End Device configuration

XBee end devices support three different sleep modes:
Pin sleep
n
Cyclic sleep
n
Cyclic sleep with pin wake-up
n
Pin sleep allows an external microcontroller to determine when the XBee/XBee-PRO Zigbee RF
Module sleeps and when it wakes 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. Cyclic sleep with pin
wake-up is the same as cyclic sleep except the device can be awakened before the sleep period
expires by lowering the SLEEP_RQ line. The SM command configures the sleep mode.
In both pin and cyclic sleep modes, XBee end devices poll their parent every 100 ms while they are
awake to retrieve buffered data. When the end device sends a poll request, it enables the receiver
until it receives an acknowledgment from the parent. It typically takes less than 10 ms between
sending the poll request to receiving the acknowledgment. The acknowledgment indicates if the
parent has buffered data for the end device child. If the acknowledgment indicates the parent has
pending data, the end device leaves the receiver on to receive the data. Otherwise, the end device
turns off the receiver and enter idle mode (until it sends the next poll request) to reduce current
consumption (and improve battery life).
Once the device enters sleep mode, the On/Sleep pin (TH pin 13/SMT pin 26) it de-asserts (low) to
indicate the device is entering sleep mode. If the device enables CTS hardware flow control (D7
command), it de-asserts (high) the CTS pin (TH pin 12/SMT pin 25) when entering sleep to indicate
that serial data should not be sent to the device.
If the Associate LED pin is configured (D5 command), the associate pin is driven low to avoid using
power to light the LED. The Sleep_Rq pin is configured as a pulled-down input so that an external
device must drive it low to wake the device. All other pins are left unmodified during sleep so that they
can operate as previously configured by the user. The device does 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 device wakes from sleep, it asserts (high) the On/Sleep pin, and if it enables flow control, it
also asserts (low) the CTS pin. The associate LED and all other pins resume their former configured
XBee/XBee-PRO® S2C Zigbee® RF Module
configuration.
Non-Parent device operation
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