71M6511/71M6511H
Single-Phase Energy Meter IC
DATA SHEET
AUGUST 2007
Environment
Before starting the CE using the CE_EN bit, the MPU has to establish the proper environment for the CE by implementing the
following steps:
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•
•
•
•
Loading the image for the CE code into CE PRAM.
Loading the CE data into CE DRAM.
Establishing the equation to be applied in EQU.
Establishing the accumulation period and number of samples in PRE_SAMPS and SUM_CYCLES.
Establishing the number of cycles per ADC mux cycle.
The default configuration is FIR_LEN = 1 (three cycles per conversion) and MUX_DIV = 1 (4 conversions per mux cycle).
There must be thirteen CK32 cycles (see System Timing Diagram, Figure 13). This means that the product of the number of
cycles per ADC conversion and the number of conversions per cycle must be 12 (allowing for one settling cycle).
Alternatively, the 71M6511 can be operated at ten CK32 cycles per ADC mux cycle (MUX_DIV = 2). CE quantities are stated
in this section for MUX_DIV = 2, if they differ from those associated with the default setting.
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 CHOP must be altered
for each sample. It must also alternate for each alternate multiplexer reading.
The MPU must program CHOP_EN alternately between 01 and 10 on every CE_BUSY interrupt except for the first CE_BUSY
after an XFER_BUSY interrupt. Note that when XFER_BUSY occurs, it will always be at the same time as a CE_BUSY
interrupt.
CE Calculations
The CE performs the precision computations necessary to accurately measure power. These computations include offset
cancellation, phase compensation, 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). As a function of EQU, the element components V0 through I2 take on different
meanings.
Element Input Mapping
Watt & VAR Formula
(WSUM/VARSUM)
EQU
W0SUM/
W1SUM/
I0SQSUM
IA
I1SQSUM
VAR0SUM
VAR1SUM
0
1
VA*IA
VA*IB
IB
IB
VA IA (1 element, 2W 1φ)
VA*(IA-IB)/2
(1 element, 3W 1φ)
VA*(IA-IB)/2
VA*IB
IA-IB
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