User's Manual

XBee®/XBee‐PRO®ZBRFModules
©2009DigiInternational,Inc. 84
Putting it all Together
Short Sleep Periods
Pin and cyclic sleep devices that sleep less than 30 seconds can receive data transmissions at any
time since their parent device(s) will be able to buffer data long enough for the end devices to
wake and poll to receive the data. SP should be set the same on all devices in the network. If end
devices in a network have more than one SP setting, SP on the routers and coordinators should be
set to match the largest SP setting of any end device. This will ensure the RF packet buffering, poll
timeout, and transmission timeouts are set correctly.
Extended Sleep Periods
Pin and cyclic sleep devices that might sleep longer than 30 seconds cannot receive data
transmissions reliably unless certain design approaches are taken. Specifically, the end devices
should use IO sampling or another mechanism to transmit data when they wake to inform the
network they can receive data. SP and SN should be set on routers and coordinators such that (SP
* SN) matches the longest expected sleep time. This configures the poll timeout so end devices
are not expired from the child table unless a poll request is not received for 3 consecutive sleep
periods.
As a general rule of thumb, SP and SN should be set the same on all devices in almost all cases.
Sleep Examples
This section covers some sample XBee configurations to support different sleep modes. Several AT
commands are listed with suggested parameter values. The notation in this section includes an '='
sign to indicate what each command register should be set to - for example, SM=4. This is not the
correct notation for setting command values in the XBee. In AT command mode, each command is
issued with a leading 'AT' and no '=' sign - for example ATSM4. In the API, the two byte command
is used in the command field, and parameters are populated as binary values in the parameter
field.
Example 1
Configure a device to sleep for 20 seconds, but set SN such that the On/Sleep line will
remain de-asserted for up to 1 minute.
The following settings should be configured on the end device.
SM = 4 (cyclic sleep) or 5 (cyclic sleep, pin wake)
SP = 0x7D0 (2000 decimal). This causes the end device to sleep for 20 seconds since SP is
measured in units of 10ms.
SN = 3. (With this setting, the On/Sleep pin will assert once every 3 sleep cycles, or when RF data
is received)
SO = 0
All router and coordinator devices on the network should set SP to match SP on the end device.
This ensures that RF packet buffering times and transmission timeouts will be set correctly.
Since the end device wakes after each sleep period (ATSP), the SN command can be set to 1 on all
routers and the coordinator.
Example 2
Configure an end device to sleep for 20 seconds, send 4 IO samples in 2 seconds, and
return to sleep.
Since SP is measured in 10ms units, and ST and IR are measured in 1ms units, configure an end
device with the following settings:
SM = 4 (cyclic sleep) or 5 (cyclic sleep, pin wake)
SP = 0x7D0 (2000 decimal). This causes the end device to sleep for 20 seconds.