Data Sheet AS8118

Revision 1.8, 15-Feb-05

Page 11 of 30

Direction Input (DIRI)

The direction input pin (DIRI) is used to program the AS8118 for either bi-directional energy measurement, or unidirectional

measurement.

Bi-directional measurement mode ensures that all energy is measured regardless of the direction of the current through the

current sensor. In unidirectional energy measurement mode, all negative going energy is suppressed and thus excluded from

the accumulated energy value.

The programming conditions for the DIRI pin are given below:

DIRI Pin

Mode

0

Unidirectional

1

Bi-directional

The default condition, when the DIRI pin is not connected is bi-directional energy measurement, as the DIRI pin has an on-

chip pull-up resistor.

Direction Output (DIRO)

The Direction Output pin (DIRO) is a logic output providing information on the direction of the current flow through the current

sensor. The DIRO output may be used to directly drive an LED to indicate a reversal in the direction of current flow.

The timing diagram below demonstrates the operation of the DIRO output and the pulse outputs (MOP/MON, CAL and LED)

relative to the sign of the measured energy and the setting of the DIRI input.

For illustration purposes, the timing diagram below only shows the LED output.

VP

IP

DIRI

LED

DIRO

1

4

3

2

Figure 5

Timing diagram for the DIRI and DIRO functions

The timing diagram above demonstrates the state of both the LED and DIRO output pins depending on the input conditions:

1.

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

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