The STPM01 is designed for effective measurement of active, reactive and apparent energy in a power line system using Rogowski coil, current transformer and shunt sensors. This device can be implemented as a single chip monophase energy meter or as a peripheral measurement in a microcontroller based monophase or 3-phase energy meter. The STPM01 consists, essentially, of two parts: the analog part and the digital part. The former, is composed by preamplifier and 1storder Δ ∑ A/D converter blocks, band gap voltage reference, low drop voltage regulator, the latter, is composed by system control, oscillator, hard wired DSP and SPI interface. There is also an OTP block, which is controlled through the SPI by means of a dedicated command set. The configured bits are used for testing, configuration and calibration purpose. From a pair of Δ ∑ output signals coming from analog section, a DSP unit computes the amount of consummated active, reactive and apparent energy, RMS and instantaneous values of voltage and current. The results of computation are available as pulse frequency and states on the digital outputs of the device or as data bits in a data stream, which can be read from the device by means of SPI interface. This system bus interface is used also during production testing of the device and/or for temporary or permanent programming of bits of internal OTP. In the STPM01 an output signal with pulse frequency proportional to energy is generated, this signal is used in the calibration phase of the energy meter application allowing a very easy approach. When the device is fully configured and calibrated, a dedicated bit of OTP block can be written permanently in order to prevent accidental entering into some test mode or changing any configuration bit.