Cyclic Sleep Mode (SM = 4 - 8)

Cyclic Sleep modes allow device wakes according to the times designated by the cyclic sleep settings. If the device detects a wake-up initializer during the time it is awake, the device synchronizes with the transmitting device and receives data after the wake-up initializer runs its duration. Otherwise, the device returns to Sleep mode and continues to cycle in and out of activity until a wake-up initializer is detected.

While the device is in Cyclic Sleep mode, it de-asserts (high) CTS (pin 25) to indicate not to send data to the device. When the device awakens to listen for data, it asserts CTS and transmits any data received on the DI pin. The device also de-asserts (low) the TX_PWR (pin 28) when it is in Cyclic Sleep mode.

The device remains in Sleep mode for a user-defined period of time ranging from 1 second to 16 seconds (SM parameters 4 through 8). After this interval of time, the device returns to Idle mode and listens for a valid data packet. The listen time depends on the BR parameter setting. The default BR setting of 1 requires at least a 35 ms wake time, while the BR setting of 0 requires a wake time of up to 225 ms. If the device does not detect valid data on any frequency, it returns to Sleep mode. If it detects valid data, it transitions into Receive mode and receives the incoming RF packets. The device then returns to Sleep mode after a period of inactivity determined by the ST parameter.

You can also configure the device to wake from cyclic sleep when the SLEEP pin is de-asserted. To configure a device to operate in this manner, you must send the PW (Pin Wake-up) command. When you de-assert the SLEEP pin, it forces the device into Idle mode and it can begin transmitting or receiving data. It remains active until it no longer detects data for the time that ST specifies, at which point it resumes its low-power cyclic state.

Cyclic scanning

Each RF transmission consists of an RF initializer and payload. The RF initializer contains initialization information and all receiving devices must wake during the wake-up initializer portion of data transmission in order to synchronize with the transmitting device and receive the data.

The cyclic interval time defined by the SM (Sleep Mode) command must be shorter than the interval time defined by LH (Wake-up Initializer Timer) command.

Correct configuration (LH > SM)

In the following figure, the length of the wake-up initializer exceeds the time interval of Cyclic Sleep. The receiver is guaranteed to detect the wake-up initializer and receive the accompanying payload data.

The LH (Wakeup Initializer Timer) is only enabled if the HT (Time before Wake-up Initializer) is non-default. The Wakeup Initializer is resent at the beginning of every packet unless the HT is set. Set HTless than or equal to the ST (Wake Time) such that once the XTC RF Module has received the Wakeup Initializer, another Wakeup Initializer need not be sent again until the expiration of the ST has expired.

Incorrect configuration (LH < SM)

Length of wake-up initializer is shorter than the time interval of Cyclic Sleep. This configuration is vulnerable to the receiver waking and missing the wake-up initializer (and therefore also the accompanying payload data).