71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
During operation, the MPU is in charge of controlling the multiplexer cycles, for example by inserting an alternate multiplexer
sequence at regular intervals using MUX_ALT. This enables temperature measurement. The polarity of chopping circuitry must
be altered for each sample. It must also alternate for each alternate multiplexer reading. This is accomplished by maintaining
CHOP_E = 00.
CE Calculations
The CE performs the precision computations necessary to accurately measure energy. These computations include offset
cancellation, products, product smoothing, product summation, frequency detection, VAR calculation, sag detection, peak
detection, and voltage phase measurement. All data computed by the CE is dependent on the selected meter equation as
given by EQU (in I/O RAM). Although EQU=0 and EQU=2 have the same element mapping, the MPU code can use the value
of EQU to decide if element 2 is used for tamper detection (typically done by connecting VB to VA) or as a second independent
element.
Element Input Mapping
Watt & VAR Formula
EQU
W0SUM/
VAR0SUM
W1SUM/
VAR1SUM
(WSUM/VARSUM)
I0SQSUM
I1SQSUM
VA IA (1 element, 2W 1φ)
0
1
2
VA*IA
VA*(IA-IB)/2
VA*IA
VA*IB
VA*IB/2
VB*IB
IA
IA-IB
IA
IB
IB
IB
with tamper detection
VA*(IA-IB)/2
(1 element, 3W 1φ)
VA*IA + VB*IB
(2 element, 4W 2φ)
CE STATUS
Since the CE_BUSY interrupt occurs at 2520.6Hz, it is desirable to minimize the computation required in the interrupt handler
of the MPU. The MPU can read the CE status word at every CE_BUSY interrupt.
CE
Address
Name
CESTATUS
Description
0x7A
See description of CE status word below
The CE Status Word is used for generating early warnings to the MPU. It contains sag warnings for VA as well as F0, the
derived clock operating at the fundamental input frequency. CESTATUS provides information about the status of voltage and
input AC signal frequency, which are useful for generating early power fail warnings, e.g. to initiate necessary data storage.
CESTATUS represents the status flags for the preceding CE code pass (CE busy interrupt). Sag alarms are not remembered
from one code pass to the next. The CE Status word is refreshed at every CE_BUSY interrupt.
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