Description

The AS8268 is highly integrated CMOS single-phase energy metering devices for fully electronic LCD meter systems. The AS8268 has been designed to ensure a meters full compliance with the international Standards IEC62052 and ANSI.

The AS8268 IC includes all the functions required for conventional 1 current or 2-current anti-tamper meters. The functions include precision energy measurement, an 8-bit microcontroller unit (MCU) with 32kBytes of Flash memory, an on-chip Liquid Crystal Display driver (LCDD), programmable multi-purpose Inputs/Outputs (MPIO), a real time clock/calendar (RTC) for complex tariff functions such as time-of-use or maximum demand billing and a Serial Peripheral Interface (SPI) for reading data from and writing data to an optional external non-volatile memory (EEPROM).

The AS8268 IC has a dedicated energy measurement front-end, which includes an analog front-end and programmable Digital Signal Processor (DSP) from which active energy, mains voltage and mains current are provided. Reactive and apparent energy can also be calculated.

The on-chip 8-bit 8051 compatible microcontroller is freely programmable and provides user access to the various functional blocks. The dedicated Universal Asynchronous Receiver / Transmitter (UART1) in the System Control block allows access to various system functions and blocks. A second UART (UART2) is also provided, which may for example be used for debugging. The on-chip memory includes 32kByte of highly reliable non-volatile Flash program (and data) memory and 1kByte volatile data memory. The meter system designer also has the option of an additional external EEPROM memory, which is selectable in size from 1kByte to 32kByte (in binary steps).

Program and data stored in the on-chip non-volatile Flash memory can be secured by password protection, in addition to an attack counter which ‘locks’ access after 5 unauthorised attacks.

An on-chip programmable watchdog timer (WDT) is available to automatically initiate a system reset if a regular ‘hold-off’ signal is not detected.

The system timing and real time clock (RTC) has a dedicated external battery supply pin (VDD_BAT), enabling the oscillator and RTC to continue operation during ‘power-down’. The RTC may be digitally calibrated for oscillator frequency accuracy.

The on-chip temperature sensor provides the meter designer the option of temperature compensation for any of the measured parameters or functional blocks provided, over the full operating temperature range of the device.

The 96-segment LCD Driver (LCDD) block enables the display of information provided by the microcontroller, directly to the LCD. Two dedicated data register banks are provided to simplify programming, particularly in the case where scrolled display data is required.

The 12 programmable multi-purpose I/O pins (MPIO) may be independently configured as inputs or outputs. All the I/O pins are programmable for data direction, pull-up/pull-down resistors and drive strength (4mA/8mA). Typical functions may include LED energy consumption pulse output, energy direction and fault condition indication depending on current 1 or current 2 being active for the energy calculation, push button for display scrolling, mains isolation relay control for prepayment meters, optical interface etc.

An on-chip analog ground buffer (ABUF) and voltage reference (VREF) ensures that no external circuitry is required. A power-supply monitor (PSM) provides a reset, when VDD falls below a safe operating threshold.

A reset pin (RES_N) is available for external system reset.