User Manual

XBee®/XBee‐PRO®RFModules‐802.15.4‐v1.xEx[2011.06.1]
©2011DigiInternatonal,Inc. 26
low. When waking the module, the pin must be de-asserted at least two 'byte times' after CTS
goes low. This assures that there is time for the data to enter the DI buffer.
Cyclic Sleep Modes
Cyclic Sleep Remote (SM = 4)
• Typical Power-down Current: < 50 µA (when asleep)
• Typical wake-up time: 2.6 msec
The Cyclic Sleep Modes allow modules to periodically check for RF data. When the SM parameter is
set to ‘4’, the module is configured to sleep, then wakes once a cycle to check for data from a
module configured as a Cyclic Sleep Coordinator (SM = 0, CE = 1). The Cyclic Sleep Remote sends
a poll request to the coordinator at a specific interval set by the SP (Cyclic Sleep Period) parame-
ter. The coordinator will transmit any queued data addressed to that specific remote upon receiv-
ing the poll request.
If no data is queued for the remote, the coordinator will not transmit and the remote will return to
sleep for another cycle. If queued data is transmitted back to the remote, it will stay awake to
allow for back and forth communication until the ST (Time before Sleep) timer expires.
Also note that CTS
will go low each time the remote wakes, allowing for communication initiated
by the remote host if desired.
Cyclic Sleep Remote with Pin Wake-up (SM = 5)
Use this mode to wake a sleeping remote module through either the RF interface or by the de-
assertion of Sleep_RQ for event-driven communications. The cyclic sleep mode works as described
above (Cyclic Sleep Remote) with the addition of a pin-controlled wake-up at the remote module.
The Sleep_RQ pin is edge-triggered, not level-triggered. The module will wake when a low is
detected then set CTS
low as soon as it is ready to transmit or receive.
Any activity will reset the ST (Time before Sleep) timer so the module will go back to sleep only
after there is no activity for the duration of the timer. Once the module wakes (pin-controlled), fur-
ther pin activity is ignored. The module transitions back into sleep according to the ST time
regardless of the state of the pin.
[Cyclic Sleep Coordinator (SM = 6)]
• Typical current = Receive current
• Always awake
NOTE: The SM=6 parameter value exists solely for backwards compatibility with firmware version
1.x60. If backwards compatibility with the older firmware version is not required, always use the CE
(Coordinator Enable) command to configure a module as a Coordinator.
This mode configures a module to wake cyclic sleeping remotes through RF interfacing. The Coor-
dinator will accept a message addressed to a specific remote 16 or 64-bit address and hold it in a
buffer until the remote wakes and sends a poll request. Messages not sent directly (buffered and
requested) are called "Indirect messages". The Coordinator only queues one indirect message at a
time. The Coordinator will hold the indirect message for a period 2.5 times the sleeping period
indicated by the SP (Cyclic Sleep Period) parameter. The Coordinator's SP parameter should be set
to match the value used by the remotes.