An internal BOR circuit monitors the VDDIO rail for dips in voltage which result in the supply voltage dropping out of operational range. When the VDDIO voltage drops below the BOR threshold, the device is forced into reset, and XRSn is pulled low. XRSn will remain in reset until the voltage returns to the operational range. The BOR is enabled by default. To disable the BOR, set the BORLVMONDIS bit in the VMONCTL register. The internal BOR circuit monitors only the VDDIO rail. See Section 5.6 for BOR characteristics. External supply voltage supervisor (SVS) devices can be used to monitor the voltage on the 3.3-V and 1.2-V rails and to drive XRSn low if supplies fall outside operational specifications.