Sleep Parameters - Digi XBee S2C 802.15.4 User Manual

Radio frequency module

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Operation

Sleep mode

SM 0

SM 1

SM 4

SM 5

Pin Sleep mode (SM = 1)

Pin Sleep mode minimizes quiescent power (power consumed when in a state of rest or inactivity).

This mode is voltage level-activated; when Sleep_RQ (pin 9 for through-hole, pin 10 for surface-mount)

is asserted, the device finishes any transmit, receive or association activities, enters Idle mode, and

then enters a state of sleep. The device does not respond to either serial or RF activity while in pin

sleep.

To wake a sleeping device operating in Pin Sleep mode, de-assert Sleep_RQ. The device wakes when

Sleep_RQ is de-asserted and is ready to transmit or receive when the CTS line is low. When waking

the device, 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 mode (SM = 4)

The Cyclic Sleep modes allow devices to periodically check for RF data. When the SM parameter is set

to 4, the XBee/XBee-PRO S2C 802.15.4 RF Module is configured to sleep, then wakes once per cycle to

check for data from a coordinator. The Cyclic Sleep Remote sends a poll request to the coordinator at

a specific interval set by the SP (Cyclic Sleep Period) parameter. The coordinator transmits any

queued data addressed to that specific remote upon receiving the poll request.

ON_SLEEP goes high and CTS goes low each time the remote wakes, allowing for communication

initiated by the remote host if desired.

Cyclic Sleep with Pin Wake-up mode (SM = 5)

Use this mode to wake a sleeping remote device through either the RF interface or by de-asserting

SLEEP_RQ for event-driven communications. The cyclic sleep mode works as described previously with

the addition of a pin-controlled wake-up at the remote device. The SLEEP_RQ pin is level-triggered.

The device wakes when a low is detected then set CTS low as soon as it is ready to transmit or

receive.

Any activity resets the ST (Time before Sleep) timer, so the device goes back to sleep only after there

is no activity for the duration of the timer. Once the device wakes (pin-controlled), it ignores further

pin activity. The device transitions back into sleep according to the ST time regardless of the state of

the pin.