71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
CE Interface Description
CE Program
The CE program is supplied by TERIDIAN as a data image that can be merged with the MPU operational code for meter
applications. Typically, the CE program covers most applications and does not need to be modified. The description in this
section applies to CE code revision CE6521BE_A04.
Formats
All CE words are 4 bytes. Unless specified otherwise, they are in 32-bit two’s complement (-1 = 0xFFFFFFFF). ‘Calibration’
parameters are defined in flash memory (or external EEPROM) and must be copied to CE data memory by the MPU before
enabling the CE. ‘Internal’ variables are used in internal CE calculations. ‘Input’ variables allow the MPU to control the behavior
of the CE code. ‘Output’ variables are outputs of the CE calculations.
Constants
Constants used in the CE Data Memory tables are:
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FS = 32768Hz/13 = 2520.62Hz.
F0 is the fundamental frequency.
IMAX is the external rms current corresponding to 250mV pk at the inputs IA and IB.
VMAX is the external rms voltage corresponding to 250mV pk at the VA and VB inputs.
NACC, the accumulation count for energy measurements is PRE_SAMPS*SUM_CYCLES.
Accumulation count time for energy measurements is PRE_SAMPS*SUM_CYCLES/FS.
The system constants IMAX and VMAX are used to convert internal quantities (as used by the CE) to external, i.e. metering
quantities. Their values are determined by the off-chip scaling of the voltage and current sensors used in an actual meter. The
LSB values used in this document relate digital quantities at the CE interface to external meter input quantities. For example, if
a SAG threshold of 80V peak is desired at the meter input, the digital value that should be programmed into SAG_THR would
be 80V/SAG_THRLSB, where SAG_THRLSB is the LSB value in the description of SAG_THR.
The parameters EQU, CE_E, PRE_SAMPS, and SUM_CYCLES essential to the function of the CE are stored in I/O RAM (see I/O
RAM section).
Environment
Before starting the CE using the CE_E bit, the MPU has to establish the proper environment for the CE by implementing the
following steps:
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Load the CE data into CE DRAM.
Establish the equation to be applied in EQU.
Establish the accumulation period and number of samples in PRE_SAMPS and SUM_CYCLES.
Establish the number of cycles per ADC mux frame.
Set PLS_INTERVAL[7:0] to 81.
Set FIR_LEN to 1 and MUX_DIV to 1.
There must be thirteen 32768Hz cycles per ADC mux frame (see System Timing Diagram, Figure 16). This means that the
product of the number of cycles per frame and the number of conversions per frame must be 12 (allowing for one settling
cycle). The required configuration is FIR_LEN = 1 (three cycles per conversion) and MUX_DIV = 1 (4 conversions per mux
frame).
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.
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