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XBee® Wi-Fi RF Modules

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

UART data can be received in pin sleep mode, whether or not the host asserts the

SleepRq pin. For example, if RF data is received by the module while SleepRq is

asserted, the module will wake up long enough to send the data out the UART and then

immediately resume sleeping. Note that if wake host is configured, the module will

assert the appropriate I/O lines (indicating that it is awake), then wait for wake host

timer to expire, then output the data, and then immediately resume sleeping.

In this mode, when SleepRq is asserted the module will power down the Wi-Fi circuitry.

When SleepRq is de-asserted, the Wi-Fi circuitry is powered up. This causes the module

to associate to the access point for each wake event. If the module was associated

when it went to sleep, it should be ready to transmit data as soon as the On/Sleep pin

indicates that the module is awake. If the module was not associated when it went to

sleep, the host must wait until the module is associated before a transmission can occur.

(In API mode, a modem status frame will be received when the module becomes

associated. Outside of API mode, the AI command must be used to determine when the

module is associated.)

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