AS8267 datasheet(15/136 Pages) AMSCO

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Data Sheet AS8267 / AS8268

Revision 1.0, 19-Jun-07

Page 15 of 136

8. Detailed Functional Description

The AS8267 / AS8268 integrated circuits have a dedicated measurement front end, which is capable of

measuring active and reactive energy, RMS mains voltage, RMS mains current as well as power factor. There

are two completely separate differential current channel inputs, for measurement of both the Live and Neutral

currents. The two current inputs may be connected to a shunt resistor (I1) and a current transformer (I2). Both

current channels have programmable gains; thus it is possible to connect the shunt resistor to any of the two

differential current inputs. The option to use two current transformers is also available. The AS8267 / AS8268

ICs may be programmed to accept either of the two measured currents for the energy calculation, or may be

programmed to accept the larger of the two currents for the energy calculation.

The AS8267 / AS8268 ICs may also be used for conventional 1-phase single current measurement

applications, where only the Live current is measured. In this case, the I2P and I2N pins are left unconnected

and the second current channel modulator can be powered down.

The voltage channel input for measurement of the line voltage is also differential and is connected to a tap of a

resistive divider of the line voltage. The resistive divider can be set to accommodate any line voltage standard

(Vmains) including 100V, 110V, 220V, 230V or 240V.

A 3.0 to 4.0MHz low power oscillator generates the system clock for the AS8267 / AS8268 ICs. The absolute

clock frequency may be calibrated on-chip. A low power divider is used to generate a 1Hz clock for the on-chip

real time clock/calendar (RTC). The supply voltage to the low power oscillator, the low power divider and the

RTC may be buffered with an external battery in case of mains power drops or failures.

The integrated temperature sensor can be used to compensate for temperature drift of the quartz crystal to

improve measurement accuracy.

The LCD driver (LCDD) signals LSD0 … LSD23 and LBP0 … LBP3 can be directly connected to a liquid crystal

display (LCD), which is used to display the various measured parameters. A total of 80 LCD segments may be

driven by the AS8267 IC and 96 segments may be driven by the AS8268 IC.

A maximum of 12 programmable multi-purpose input/output (MPIO) pins are available for various meter

functions, for example light-emitting diodes (LED) to signal energy consumption, energy direction, fault

condition, etc. These I/O pins may also be programmed for use as bi-directional communication channels such

as an optical interface or an additional Universal Asynchronous Receiver/Transmitter (UART2) Interface,

should it so be required. The AS8267 has 9 x MPIO pins, while the AS8268 has 12 x MPIO pins.

A dedicated Serial Peripheral Interface (SPI) which can be configured as master or slave is also provided.

In master mode an external EEPROM (1kByte up to 32kByte) with a compatible serial peripheral interface can

be connected if required.

In slave mode the interface allows direct access to the internal Flash memory.

The on-chip 8051 compatible microcontroller performs all the required calculations and enables the user to

customize the input and output configuration of the meter. The microcontroller has a 1kB data memory, a

square root calculation facility and a second UART (UART2) for debugging purposes.

The highly reliable 32kByte Flash memory allows storage of program and data. With the integrated security

concept Flash Data can be protected against unauthorised access. The security concept offers password

protection as well as an attack counter which blocks the Flash after five unauthorised attacks.

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