Digi XBee DigiMesh 2.4, Руководство пользователя

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Sleep modes Synchronous cyclic sleep mode
XBee/XBee-PRO DigiMesh 2.4 RF Module User Guide 61
Synchronous cyclic sleep mode
Set SM to 8 to enter synchronous cyclic sleep mode.
A device in synchronous cyclic sleep mode sleeps for a programmed time, wakes in unison with other
nodes, exchanges data and sync messages, and then returns to sleep. While asleep, it cannot receive
RF messages or receive data (including commands) from the UART port.
Generally, the network’s sleep coordinator specifies the sleep and wake times based on its SP and ST
settings. The device only uses these parameters at startup until the device synchronizes with the
network.
When a device has synchronized with the network, you can query its sleep and wake times with the
OS and OW commands respectively.
If D9 = 1 (ON_SLEEP enabled) on a cyclic sleep node, the ON_SLEEP line asserts when the device is
awake and de-asserts when the device is asleep.
If D7 = 1, the device de-asserts CTS while asleep.
A newly-powered, unsynchronized, sleeping device polls for a synchronized message and then sleeps
for the period that the
SP command specifies, repeating this cycle until it synchronizes by receiving a
sync message. Once it receives a sync message, the device synchronizes itself with the network.
Note Configure all nodes in a synchronous sleep network to operate in either synchronous sleep
support mode or synchronous cyclic sleep mode. asynchronous sleeping nodes are not compatible
with synchronous sleeping nodes.
The sleep timer
If the device receives serial or RF data in Asynchronous cyclic sleep mode and Asynchronous cyclic
sleep with pin wake up modes (
SM = 4 or SM = 5), it starts a sleep timer (time until sleep).
n
If the device receives any data serially or by RF link, the timer resets.
n
Use ST (Wake Time) to set the duration of the timer.
n
When the sleep timer expires the device returns to sleep.
Sleep coordinator sleep modes in the DigiMesh network
In a synchronized sleeping network, one node acts as the sleep coordinator. During normal
operations, at the beginning of a wake cycle the sleep coordinator sends a sync message as a
broadcast to all nodes in the network. This message contains synchronization information and the
wake and sleep times for the current cycle. All cyclic sleep nodes that receive a sync message remain
awake for the wake time and then sleep for the specified sleep period.
The sleep coordinator sends one sync message at the beginning of each cycle with the current wake
and sleep times. All router nodes that receive this sync message relay the message to the rest of the
network. If the sleep coordinator does not hear a rebroadcast of the sync message by one of its
immediate neighbors, then it re-sends the message one additional time.
If you change the SP or ST parameters, the network does not apply the new settings until the
beginning of the next wake time. For more information, see Change sleep parameters .
A sleeping router network is robust enough that an individual node can go several cycles without
receiving a sync message, due to RF interference, for example. As a node misses sync messages, the
time available for transmitting messages during the wake time reduces to maintain synchronization
accuracy. By default, a device reduces its active sleep time progressively as it misses sync messages.