AS8267 datasheet(27/136 Pages) AMSCO

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Data Sheet AS8267 / AS8268

Revision 1.0, 19-Jun-07

Page 27 of 136

from positive energy, thus when DIRO = 1, the negative energy is converted to positive energy by the ‘Abs’

block shown in Figure 3:

AFE block diagram.

Should the meter application require unidirectional energy measurement, the MCU can separately derive both

the positive and negative energy values, depending on the status of the DIRO bit.

Accumulator for Real Power (P_ACCU)

To ensure that the power information transferred to the MCU is identical to that of the LED pulses, the P_ACCU

counts the pulses generated by Fast Pulse Gen. After ‘nsamp’ (nyquist) sampling periods an interrupt is sent to

the MCU requesting to fetch the new energy information. (Interrupt line ‘IE.0’ goes high and the ‘data available

interrupt’ (dai) flag in the SREG/Status register is set). The ‘ack’ bit in the SREG/Status register is also set to

1. If the MCU takes the energy information, it has to reset the ‘ack’ bit signalling that the energy information

has been taken. If the ‘ack’ bit is not reset the P_ACCU will add the ‘old’ energy information to the ‘new’ energy

information accumulated in the following cycle.

In any event, the MCU must reset the dai flag in order to clear the interrupt.

Wait for

fast pulse

Increment

P_ACCU

np = 0

New fast

pulse?

np = P_ACCU + np (old)

P_ACCU = 0

nsamp

reached?

IE.0 = 1

dai = 1

ack = 1

ack = 0?

Note: The above flow chart assumes that the dai flag is always reset in time before the next interrupt is

generated.

Pulse Generation

Two pulse generators are provided to ensure that virtually any LED pulse rate output can be programmed for

display and calibration purposes. The first pulse generator (Fast Pulse Gen) produces fast internal pulses.

These fast pulses are accumulated in the power accumulator (P_ACCU) for energy data transfer to the MCU.

AS8267 датащи(PDF) 27 Page - ams AG