User Manual

XBee® Wi-Fi RF Modules

19 is to indicate when the XBee has data to send to the host, it may legitimately be

driven high or low while the module is awake.

When using the SPI, either SleepRq or SPI_nSSEL may be used for pin sleep. If D8 is

configured as a peripheral (1), then it will be used for pin sleep. If not, and SPI_nSSEL is

configured as a peripheral (which it must be to enable SPI operation), then SPI_nSSEL is

used for pin sleep.

Using SPI_nSSEL for pin sleep has the advantage of requiring one less physical pin

connection to implement pin sleep on SPI. It has the disadvantage of putting the radio

to sleep whenever the SPI master negates SPI_nSSEL, even if that wasn't the intent.

Therefore, if the user can control SPI_nSSEL, whether or not data needs to be

transmitted, then sharing the pin may be a good option. It makes the SleepRq pin

available for another purpose, or it simply requires one less pin to the SPI interface.

Sleep Options

AP Associated Sleep

This option allows the module to sync up with beacons sent from the AP which contains

the DTIM (Delivery Traffic Indication Message). The DTIM indicates when broadcast and

multicast data will be sent on the network. This property is configured on the AP and is

typically configured as the number of beacons between each beacon with DTIM. The

current draw in associated sleep mode varies significantly. When the module is awake it

draws approximately 100 mA. When it is asleep, it draws approximately 2 mA. Total

current draw increases when the DTIM rate is higher and it decreases when the DTIM

rate is lower on the access point.

The sleep modes are described as follows with this option enabled.

Pin Sleep Mode

The module remains associated to the AP and will wake based on the period of the

DTIM. This wake period will not be seen by the local host unless data has been sent to

the module. In this case the module will ‘wake’ by asserting the appropriate I/O lines.

The local UART host is then required to de-assert the sleep pin (either SleepRq

SPI_nSSEL) to awaken the module. Once the sleep pin is de-asserted the module will

then send the data to the host.

SPI operation is similar except that the radio asserts nATTN when data becomes

available and then the local host is expected to assert SPI_nSSEL and to provide a clock

until the data available is sent out.

When the local UART host needs to send data it de-asserts SleepRq. Once the

appropriate status I/O lines are asserted (CTS and/or On/nSleep) the module is ready to

accept data. However data will be queued and not sent until the next DTIM.

When the local SPI host needs to send data it asserts SPI_nSSEL. If SPI_nSSEL is being

used for pin sleep, asserting SPI_nSSEL is enough to awaken the module to receive the