The ADE7756 contains a sampled Waveform register and an Active Energy register capable of holding at least five seconds of accumulated power at full load. Data is read from the ADE7756 via the serial interface. The ADE7756 also provides a pulse output (CF) with a frequency that is proportional to the active power. In addition to real power information, the ADE7756 also provides system calibration features, i.e., channel offset correction, phase calibration, and power calibration. The part also incorporates a detection circuit for short duration low voltage variations or sags. The voltage threshold level and the duration (in number of halfline cycles) of the variation are user programmable. An open drain logic output (SAG) goes active low when a sag event occurs. A zero crossing output (ZX) produces an output that is synchronized to the zero crossing point of the line voltage. This output can be used to extract timing or frequency information from the line. The signal is also used internally to the chip in the calibration mode. This permits faster and more accurate calibration of the real power calculation. This signal is also useful for synchronization of relay switching with a voltage zero crossing, thus improving the relay life by reducing the risk of arcing. The interrupt request output is an open drain, active low logic output. The IRQ output will become active when the accumulated real power register is half-full and also when the register overflows. A status register indicates the nature of the interrupt.