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SA9604

THREE PHASE BIDIRECTIONAL POWER/ENERGY METERING IC WITH SERIAL SPI INTERFACE

South African Micro Electronic Systems 

SA9604A

6. Register Values

The 24 bit registers are up/down counters, which increment or decrement at a rate

of 640k/s (640k*2/PI for reactive) at rated conditions. The energy register values will

increment for positive energy flow and decrement for negative energy flow as can

be seen in the following diagram:

register wrap around

Register values

positive energy flow

0 ............... H7FFFFF H800000 ............... HFFFFFF

(8388607) (8388608)

(16777215)

negative energy flow

register wrap around

At power-up the register values are underfined and for this reason the msb of the

delta value (delta value = present register value - previous register value) should

be regarded as an indication of the measured energy direction. (0 = positive, 1 =

negative).

The delta value for the energy registers is between 0 and 8388607 for positive

energy flow and between 0 and -8388607 for negative energy flow. For voltage the

maximum usable delta value is 16777215 as voltage is in a positive direction only.

When reading the registers care should be taken to check for a wrap around

condition.

As an example lets assume that with a constant load connected the delta value is

22260. Because of the constant load, the delta value should always be 22260 every

time the register is read and the previous value subtracted (assuming the same time

12/20

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