The purpose of the POR is to create a clean reset throughout the device during the entire power-up procedure. The trip point is a looser, lower trip point than the BOR, which watches for dips in the VDD or VDDIO rail during device operation. The POR function is present on both VDD and VDDIO rails at all times. After initial device power-up, the BOR function is present on VDDIO at all times, and on VDD when the internal VREG is enabled (VREGENZ pin is tied low). Both functions tie the XRS pin low when one of the voltages is below its respective trip point. Additionally, when the internal voltage regulator is enabled, an overvoltage protection circuit will tie XRS low if the VDD rail rises above its trip point. See Section 5.5 for the various trip points as well as the delay time for the device to release the XRS pin after the undervoltage or overvoltage condition is removed. Figure 6-5 shows the VREG, POR, and BOR. To disable both the VDD and VDDIO BOR functions, a bit is provided in the BORCFG register. For details, see the System Control and Interrupts chapter of the TMS320x2805x Piccolo Technical Reference Manual.