Pin sleep mode
Set SM to 1 to enter pin sleep mode.
Pin sleep allows the device to sleep and wake according to the state of the SLEEP_RQ pin (SLEEP_RQ).
When you assert SLEEP_RQ (high), the device finishes any transmit or receive operations, closes any active connection, and enters a low-power state.
When you de-assert SLEEP_RQ (low), the device wakes from pin sleep.