Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 12 of 30

2.

The voltage input (VP) and current input (IP) are in phase and the direction input DIRI is set to ‘Bidirectional’ mode.

Pulses are available at the LED output and DIRO indicates a positive energy flow.

3.

The voltage input (VP) and current input (IP) are out of phase and the direction input DIRI is set to ’Unidirectional’

mode. Pulses are no longer available at the LED output as negative going energy is not measured. The direction

output DIRO indicates a change in direction of the input current at IP.

4.

The voltage input (VP) and current input (IP) are out of phase. The direction input DIRI is set to ‘Bidirectional’ mode.

Pulses are again available at the LED output and the direction output DIRO indicates a change in direction of the

input current at IP.

Crystal Oscillator

The AS8118 has an on-chip crystal oscillator, with the recommended 3.5795MHz crystal connected to the XIN (Crystal Input)

and XOUT (Crystal Output) pins. The 3.5795MHz crystal is recommended, as it is a standard low cost component.

Alternatively, an external clock signal may be applied to XIN. In this case, XOUT should not be connected.

Test Mode (TM)

On ‘power up’, the test mode input defines the mode of operation of the device. Either ‘Normal Operation’, or ‘Programming’

modes may be selected. TM has an on-chip pull down resistor and should be left unconnected during ‘Normal Operation’. TM

must be set to logic ‘1’ at ‘power up’ to set device in ‘Programming’ mode.

The AS8118 programming procedure is defined in detail in the following paragraphs.

Power Supply Monitor

The AS8118 has an on-chip power supply monitor (PSM) which resets the complete device once the supply voltage drops

below the specified threshold of 3.5V ±5%.

Programming the AS8118

The AS8118 is a programmable device, which uses on-chip zener diodes to permanently program specific data such as

current input channel gain, pulse-level, meter constant settings and system calibration. This programming operation is also

called ‘burn’ which relates to the permanent physical change of the on-chip zener diodes electrical behavior. Another term for

‘permanent programming’ is OTP (One-Time-Programming).

Two banks of zener diodes are available in the AS8118 in order to allow a second calibration. By programming the 2nd bank

of zener diodes, this bank will subsequently be used (bank-select-bit). During power-up of AS8118, a readout of all zener

diodes occurs and the data of the active bank is used.

The AS8118 may also be used with the default operating parameters, which have been defined earlier in this document. If

the user wishes to alter the operating parameters, the AS8118 may simply be programmed to provide the required operating

parameters. Fast meter system calibration may also be carried out as part of the AS8118 programming procedure, providing

long term meter system stability.

The AS8118 can be operated in one of two modes. The two modes are:

-

Normal Operation Mode: Normal operation is the mode in which the device operates to perform the kWh metering

function, for which the device is designed.

-

Programming Mode: Programming is the mode in which the AS8118 is set to perform the programming operations. When

in Programming mode, two different operations may be carried out: