Q: FAQ: Basic procedure for entering/exiting SLEEP state in CC110x/CC1150/CC2500/CC2550. by 611949

Before commanding the radio into SLEEP state it must initially be in IDLE state. A simple SPWD strobe command is then sufficient
to initiate the SLEEP state entry, which takes effect after the CSn is pulled high. To save current in SLEEP state, the GDOx pins should
be tri-stated in advance (done via the IOCFGx registers).

To wake the radio up from SLEEP state simply pull CSn low. After pulling CSn low the interfacing MCU must wait for the CHIP_RDYn signal
to go low on the SO line, indicating that the crystal is stable (~150 us on the CC110xEM).

Note that the TEST0/1/2 register values are not retained in SLEEP state, and thus it is necessary to re-write these registers when returning
from the SLEEP state, if the recommended values are different from the default values.