Datasheet

71M6521DE/DH/FE Data Sheet
Rev 3 Page: 83 of 107
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.
EQU
Watt & VAR Formula
(WSUM/VARSUM)
Element Input Mapping
W0SUM/
VAR0SUM
W1SUM/
VAR1SUM
I0SQSUM I1SQSUM
0
VA IA (1 element, 2W 1φ)
with tamper detection
VA*IA VA*IB IA IB
1
VA*(IA-IB)/2
(1 element, 3W 1φ)
VA*(IA-IB)/2 VA*IB/2 IA-IB IB
2
VA*IA + VB*IB
(2 element, 4W 2φ)
VA*IA VB*IB IA IB
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 Description
0x7A
CESTATUS
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.