New One-Chip 1-Phase Energy Metering ICs: With Program And Data Security And Highest Reliability


By Dave Simpson

The AS8267 and AS8268 ICs on-chip Flash memory for both program and data offer integrated system-onchip solutions for LCD meters and fulfil all utility antitamper requirements. Meter designs based on the AS8267 or AS8268 ICs require a minimum of external components, ensuring optimum meter reliability and the resultant reduction in meter system cost.

The AS8268 provides for up to 96 LCD segments and 12 programmable inputs/outputs, while the AS8267 offers a lower cost solution for meters requiring up to 80 LCD segments and 9 programmable inputs/outputs.

The AS8267 and AS8268 ICs incorporate all the required functional blocks for single phase metering including a precision 2-current input energy measurement front-end, an 8-bit microcontroller, 32 kB of on-chip Flash memory, a real-time clock, up to 96-segment liquid crystal display (LCD) driver, up to 12 programmable multi-purpose inputs/outputs for all possible customer specified interface and display requirements, as well as an on-chip temperature sensor.

The extremely reliable austriamicrosystems Flash memory technology that is provided on-chip ensures program and data retention performance never before available to the metering industry in system-on-chip ICs. The Flash memory has been designed and verified to operate over the extended operating temperature range of -40ºC to +125ºC, ensuring program and data retention even under the most arduous environmental conditions. The austriamicrosystems Flash technology ensures data retention of 20 years at 125OC.

Active energy, mains voltage and mains current are calculated directly within the on-chip digital signal processor (DSP). Reactive power and apparent power is also available through user configurable application software. The precision accuracy performance of all the measured parameters provided by the AS8267 and AS8268 ICs is demonstrated through the consistent repeatability of measurements provided by these ICs. This repeatability enables production meter measurement accuracy, never before achievable and far surpasses meter specification requirements.



Performance errors of the AS8267 and AS8268 ICs

The AS8267 and AS8268 ICs provide the user the option of an additional external EEProm from 2 to 32 kB for data storage, in conjunction with the fully programmable industry standard 8-bit 8051 microcontroller (MCU) and 32 kB on-chip Flash memory. The external EEProm can be connected via a dedicated serial interface, thus none of the available inputs/outputs are required for this function. In addition to the serial interface, there are two universal asynchronous receiver transmitters (UARTs) available for all possible external communication requirements. A programmable energy LED pulse output, which precisely represents the accumulated energy data, can be accessed through any one of the multi-purpose input/outputs and is fully programmable to ensure the required pulse rate. This precision output along with an on-chip pulse counter allows the option of fast automatic digital calibration. An on-chip ±1.4 ppm real-time clock/calendar (RTC) with two alarm registers and battery back-up is available for complex tariff applications, with added precision possible through temperature tracking using the onchip temperature sensor.

All the required anti-tamper conditions have been accommodated within the AS8267 and AS8268 ICs. The three analogue front end (AFE) inputs enable full bi-directional measurement of the mains voltage and both the phase and neutral currents. This ensures that the meter can measure and record energy when all tamper connection configurations are applied including line-in and line-out interchanged, phase and neutral interchanged and missing neutral, as well as combinations of these. When current is measured and the mains voltage is unavailable for calculation, the DSP provides an option for a simulated mains voltage input to ensure the continued measurement of energy consumed.

All the inputs/outputs (MPIO) are programmable for data direction, pull-up or pull-down resistors and drive strength. This enables direct connection of LEDs to any of the MPIO for the display of reverse current, phase availability and earthing of the load, besides all other standard display requirements such as LED pulse output for calibration and consumption monitoring. The fully programmable on-chip liquid crystal display driver (LCDD) can also be used for the display of the various tamper conditions. All tamper conditions can be recorded with time and date stamp.

The AS8267 and AS8268 ICs are available in a LQFP- 64 pin package and are pin compatible with the established AS8218 and AS8228 ICs.