LR1121
User Manual Rev 1.1
UM.LR1121.W.APP Mar 2023
18 of 130
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2.1.6 Reset
Four reset sources are available to trigger a LR1121 restart and execute the startup sequence: Power-On-Reset / Brown-Out
Reset (POR/BRN), NRESET, and Reboot(...) command.
The BUSY signal is kept high during each one of the reset procedures, and returns to low when the restart procedure is
finished. At the end of the restart procedure, the device is ready to accept commands, it goes into Standby mode with RC
oscillator on (STBY_RC). All device context is lost during this operation, so the device must be re-configured and
recalibrated. POR/BRN and NRESET also trigger an authentication of the internal firmware.
2.1.6.1 Power-On-Reset and Brown-Out Reset
The LR1121 performs a restart if either of the following occurs:
• The battery voltage rises above the Power-On-Reset (POR) level
• The battery voltage temporarily drops below the Brown-Out Reset (BRN) level
Both POR and BRN trigger a full restart of the internal firmware. The Status field of the Stat2 status variable indicates if a POR
or BRN occurred.
Please refer to 5.3 Power-On-Reset and Brown-Out-Reset for addition information on the POR and BRN.
2.1.6.2 NRESET
Putting the NRESET signal to low for at least 100μs restarts the LR1121. The restart is equivalent to a Power-On Reset, and
the device follows the same restart sequence.
2.1.6.3 Reboot
Command Reboot(...) triggers a restart of the LR1121 firmware.
StayInBootLoader determines the type of reboot:
• 0: Performs a software restart
• 3: The boot-loader does not execute the firmware in flash, but allows firmware upgrades
• Other values are RFU
The 32kHz clock’s configuration is kept on a Reboot. Command ConfigLfClock(...) modifies the 32kHz clock
configuration.
Table 2-9: Reboot Command
Byte 0 1 2
Data from Host 0x01 0x18 StayInBootLoader
Data to Host Stat1 Stat2 IrqStatus (31:24)
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