The Backup subsystem operates on a dedicated power supply AUXVCC3. This subsystem includes low-frequency oscillator (XT1), RTC module, and backup RAM. The functionality of the Backup subsystem is retained during LPM3.5. The Backup subsystem module registers cannot be accessed by the CPU when the high-side SVS is disabled by user. It is necessary to keep the high-side SVS enabled with SVSHMD = 1 and SVSMHACE = 0 to turn off the low-frequency oscillator (XT1) in LPM4.