SLAU847E October 2022 – May 2025 MSPM0L1105 , MSPM0L1106 , MSPM0L1116 , MSPM0L1117 , MSPM0L1227 , MSPM0L1227-Q1 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2227-Q1 , MSPM0L2228 , MSPM0L2228-Q1
In devices with a dedicated battery backup power domain (PDB) with supply pin (VBAT), the LFSS has its VBAT power management unit (VBAT PMU) and its own reset generation circuit related to the VBAT supply pin.
Two subcircuits are related to the reset of the LFSS.
The battery backup power domain (PDB) does not experience a reset unless the power supply on the VBAT pin drops below the VBAT BOR level. The VDD BOR reset from the Main PMU does not reset the PDB domain while VBAT remains sufficiently powered.
In addition, the LFSS supports an VBAT PMU POR level software-reset request. This reset supports software development and from the LFSS point of view it looks like the VBAT supply was temporary disconnected and reconnected. This also means the PDB domain is brought down and back up and all flops have a full reset.
After the LFXT and LFSS peripherals are configured and initialized by software, a persistent status bit in the LFSS domain indicates the “running / RTC active” status to the software. On device power-up, the software reads the reset cause table and initializes the device accordingly (for example, initial power up or wake from SHUTDOWN mode). Before initializing the RTC, the software should check the LFXT and RTC good/active status and skip the initialization when already running and active.