SLAU846B June 2023 – November 2024 MSPM0G1105 , MSPM0G1106 , MSPM0G1107 , MSPM0G1505 , MSPM0G1506 , MSPM0G1507 , MSPM0G3105 , MSPM0G3106 , MSPM0G3107 , MSPM0G3505 , MSPM0G3506 , MSPM0G3507
The LFSS has its own reset generation circuit. Two subcircuits are related to the reset of the LFSS. The power-on-reset (POR) circuit is Vth based supply voltage. The POR circuit is used to reset the PMU and the startup of the cold boot sequence. The brown-out-reset (BOR) circuit is a reference-based voltage monitor and enables the LDO when the VDD supply is large enough to operate the LDO safely. On initial power up of the VDD supply and the enable of the LFSS LDO, the LFSS domain sees initial reset. When the reset is de-asserted, the LFSS domain does not see another reset unless the power supply on VDD drops below the BOR level. The BOR reset from the PMU does not reset the LFSS domain.
In addition, the LFSS supports an LFSS-POR level software-reset request. This reset supports software development and from the LFSS point of view it looks like the VDD supply was temporary disconnected and reconnected. This also means the LFSS domain is brought down and back up and all flops have a full reset.
After the LFXT and RTC 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.