
Sub-GHz radio (SUBGHZ)
RM0453
172/1454
RM0453 Rev 2
When in Standby mode, the calibration of different blocks can be requested by
Calibrate()
command.
Image calibration for specific frequency bands
The image calibration is performed as part of the calibration process, by default in the band
902 - 928 MHz. The image calibration can furthermore be requested in any band by
CalibrateImage()
command.
Image calibration must be redone when the RF frequency is changed significantly and when
the temperature changes more than 20 °C.
5.7.4 Standby
mode
The Standby mode is entered from the Calibration mode and can furthermore be entered by
Set_Standby()
command.
In Standby mode, BUSY is cleared. The software must configure the sub-GHz radio for FS,
TX, RX or Sleep mode. By default, in Standby mode, the sub-GHz radio is clocked by the
sub-GHz RC 13 MHz. For time critical applications, HSE32 can be turned on. The use of RC
13 MHz or HSE32 is selected by
Set_Standby()
command.
If the SMPS is used during the sub-GHz transmission or reception, SMPS must be enabled
in the Standby with RC 13 MHz mode. The SMPS is selected by
Set_RegulatorMode()
command. When selected, the SMPS is enabled automatically when entering the Standby
with HSE32 mode. If the SMPS has been enabled by the CPU with PWR_CR5.SMPSEN,
the SMPS remains enabled in all sub-GHz radio operating modes including transmission
and reception.
5.7.5
Frequency synthesis mode (FS)
When entering FS mode, BUSY is set. In FS mode, the RF-PLL is activated. Once RF-PLL
is locked, BUSY goes low. The sub-GHz radio may be requested to enter this mode by
Set_Fs()
.
Due to the low-IF architecture, the transmit and receive RF-PLL frequencies are different.
The receive RF-PLL frequency is equal to the transmit frequency minus the intermediate
frequency offset.
5.7.6 Transmit
mode
(TX)
The TX mode can be requested to be entered from Standby mode. In this case, the sub-
GHz radio enters first FS mode to lock the RF-PLL, and subsequently TX mode.
In TX mode after ramping-up the power amplifier (PA), data from the data buffer is
transmitted. The sub-GHz radio operates in one of the following transmit modes:
•
single transmit mode
•
single transmit with timeout mode: timeout used as safety, when the transmit is aborted
or does not succeed. The timeout informs the software of such events.
The sub-GHz radio returns automatically to Standby mode after the last data bit of the
packet is transmitted or after the timeout expires.
TX mode entry is requested by
Set_Tx()
command.