Sub-GHz radio (SUBGHZ) RM0453
172/1450 RM0453 Rev 5
5.7.1 Startup mode
At POR or after a sub-GHz radio reset, the Startup mode is entered. BUSY is set. When
internal supply and clocks become available, the sub-GHz radio enters Sleep mode.
5.7.2 Sleep mode
In Sleep mode, only the sub-GHz radio startup and Sleep control is operational and the
configuration is lost. BUSY is set. Optionally, configuration registers and memories may be
kept in retention. The RC 64 kHz and sub-GHz RTC may be kept running.
The Sleep mode provides the following sub-mode and options:
• Deep-Sleep mode: all sub-GHz radio function off, controlled by set_Sleep()
command
• Sleep with the sub-GHz radio RC 64 kHz kept on: configuration registers can be
retained as configured by Set_Sleep() command
• Sleep with the data RAM retained, controlled by Set_Sleep() command
Following a POR sub-GHz radio reset, the Deep-Sleep mode is entered from Startup mode.
Sleep mode can be entered from Standby mode by Set_Sleep() command.
Caution: After Set_Sleep() command, the sub-GHz radio cannot receive any SPI commands. The
user must guarantee that the sub-GHz radio SPI NSS is not set low during 500 μs.
Exit Sleep mode can be done:
• on a firmware request via the sub-GHz radio SPI NSS signal (keeping sub-GHz radio
SPI NSS low for at least 20 μs)
• on a request from the sub-GHz radio RTC timer generating an end-of-count event
(corresponding to duty cycled operation)
When the sub-GHz radio configuration registers are retained, a warm start is performed
when exiting Sleep mode. During a warm start, the configuration registers are restored with
their retained value an the Calibration state is skipped.
5.7.3 Calibration mode
On a cold start, when transitioning from Deep-Sleep or Sleep mode to Standby mode, the
intermediate Calibration mode is entered. In Calibration mode, BUSY is set to indicate that
the sub-GHz radio is busy and cannot accept any SPI command.
The calibration phase consists of the following operations:
• sub-GHz radio RC 64 kHz frequency calibration
• sub-GHz radio RC 13 MHz frequency calibration
• RF-PLL modulation path calibration
• RF-ADC calibration
• image calibration
The total calibration time is 1.6 ms. All calibration results are stored in data RAM.
When the data RAM is retained in Sleep mode, the sub-GHz radio retrieves the calibration
data and then transitions to Standby mode without repeating the calibration phase.
Once the calibration is finished, BUSY is deactivated and the sub-GHz radio enters Standby
with RC 13 MHz mode.
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