Power control (PWR) RM0453
238/1450 RM0453 Rev 5
the SUBGHZSPI_NSS activity, and masks the RFBUSYS status low time (not busy) after an
SPI command transfer (see the figure below).
Figure 23. Radio busy management
At reset, the radio is busy (as signaled by the RFBUSY signal). At this time, the RFBUSYMS
signal provides the same information. Subsequently the radio is woken up by a falling edge
on SUBGHZSPI_NSS. Once the radio is ready to receive a command, RFBUSYS and
RFBUSYMS go low. After reset, the RFBUSYS or RFBUSYMS status can be used to check
that the radio is ready.
For any subsequent command, as soon as the SUBGHZSPI_NSS goes low, the
RFBUSYMS status is set to signal busy radio. RFBUSYMS remains high for at least the
minimum RFBUSYMS delay after the SUBGHZSPI_NSS is set high, or as long as the
RFBUSY signal remains high:
• When transferring a command with an expected radio busy indication the RFBUSYMS
status must be used to detect the radio busy state.
• When transferring a command without any expected radio busy indication, there is no
need for checking any busy status. Anew command can be sent even when
RFBUSYMS status indicates busy radio.
When the SUBGHZSPI_NSS is selected to be driven by the LPTIM3_OUT in
PWR_CR1.SUBGHZSPINSSSEL, the RFBYSYMS status is disabled and must not be used
by software.
When in Standby mode, the CPUs can be woken up through a WRFBUSYF wake-up flag
when enabled by EWRFBUSY in Section 6.6.3: PWR control register 3 (PWR_CR3) or
Section 6.6.18: PWR CPU2 control register 3 (PWR_C2CR3).
When in Stop or Run mode, a CPU can be woken up and interrupted by the EXTI
configurable event on the RFBUSY signal, see Section 16.3.1: EXTI wake-up interrupt list.
MSv50975V1
RFBUSY/RFBUSYS
SUBGHZSPI_NSS
RFBUSYMS
POR
SUBGHZSPI_DATA
minimum RFBUSYSM delay
EXTI RFBUSY interrupt (Stop, Run)
WRFBUSYF wakeup (from Standby)
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