0: TEST1 = 0x31 and TEST2= 0x88 when waking up from SLEEP
1: TEST1 = 0x35 and TEST2 = 0x81 when waking up from SLEEP
Note that the changes in the TEST registers due to the
ADC_RETENTION bit setting are only seen INTERNALLY in the analog
part. The values read from the TEST registers when waking up from
SLEEP mode will always be the reset value.
The ADC_RETENTION bit should be set to 1before going into SLEEP
mode if settings with an RX filter bandwidth below 325 kHz are wanted at
time of wake-up.
Set the threshold for the TX FIFO and RX FIFO. The threshold is
exceeded when the number of bytes in the FIFO is equal to or higher than
the threshold value.