Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 18 of 30

Calibration without On-Chip Programming

It is also possible to calibrate a kWh meter using the AS8118 by means of an external resistor network or trim-potentiometer.

In this case, the parameters for the required pulse outputs are programmed into the device, along with the ideal value for

Pulse_lev

as defined in the formula above. A resistor network may then be used in the voltage divider for the voltage input

setting, which is then trimmed until the measured pulse rate matches the ideal pulse rate.

In the case for kWh meter designs, which include a µ-controller and non-volatile memory, again, the parameters for the

required pulse outputs are programmed into the device, along with the ideal value for Pulse_lev as defined in the formula

above. The calibration may then be performed in the µ-controller.

Defining the Programmed Word

The AS8118 allows for all on-chip programmable functions to be reprogrammed a second time. It is important to always use

the Bank ‘0‘ as the first programming option. This is necessary as once Bank ‘1‘ has been selected and this selection has

been permanently ‘Burned‘ into the AS8118 device, Bank ‘0‘ can no longer be selected.

When programming the AS8118, the Bank that is NOT selected should have all ‘0‘ values as the programmed values.

Confirmation of this is shown in the example below, where Bank ‘0‘ has been selected for programming. All the programme

bits of Bank ‘1‘ have been programmed as ‘0‘.

Important: The value of Bit [0] must always be ‘1‘ when programming the AS8118, regardless of the memory bank being

programmed. The Bits [69:68] are not used and are thus ‘Don’t Care‘ bits. The programmed value may be ‘1‘ or ‘0‘.

An example of the word to be programmed to the AS8118 should look as follows:

Bit Number

Bit Value

Description

[69:68]

00

Not used bits

[67:66]

00

Bank 1: Gain

[65:64]

00

Bank 1: Anticreep threshold

[63:62]

00

Bank 1: F_mon

[61:60]

00

Bank 1: F_cal

[59:57]

000

Bank 1: F_led

[56:35]

0x000000

Bank 1: Pulse_lev

[34:33]

00

Bank 0: Gain = 4 (CT mode)

[32:31]

01

Bank 0: Anticreep threshold = 7.43mA

[30:29]

00

Bank 0: F_mon: 100 imp/kWh

[28:27]

10

Bank 0: F_cal: Fmon x 32

[26:24]

101

Bank 0: F_led: 3200 imp/kWh

[23:2]

0x06A6D4

Bank 0: Pulse_lev: 435924

[1]

0

Select Bank 0

[0]

1

Select programmed values

After selecting all PROM parameters as required a complete 70-bit word (including two overhead bits) is formed, which must

be written to the PROM.