DS_6612_001
78M6612 Data Sheet
4.4 CE Interface Description
4.4.1 CE Program
The CE program is supplied by Teridian as a data image that can be merged with the MPU operational
code for measurement applications. Typically, the CE program covers most applications and does not
need to be modified. Other variations of CE code may be available from Teridian. The description in this
section applies to CE code revision CE6612_OMU_S2_A01_V1_2.
4.4.2 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. The corresponding MPU address for the most significant
byte is given by 0x1000 + 4 x CE_address and 0x1003 + 4 x CE_address for the least significant byte.
4.4.3 Constants
Constants used in the CE Data Memory tables are:
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FS = 32768 Hz/13 = 2520.62 Hz.
F0 is the fundamental frequency.
IMAX is the external rms current corresponding to 250 mV pk at the inputs IA and IB.
VMAX is the external rms voltage corresponding to 250 mV 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 by the MPU to convert internal quantities (as used by
the CE) to external, i.e. measurement quantities. Their values are determined by the off-chip scaling of
the voltage and current sensors used in an actual measurement unit. The LSB values used in this
document relate digital quantities at the CE or MPU interface to external measurement input quantities.
For example, if a SAG threshold of 80V peak is desired at the measurement 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 the I/O RAM section).
4.4.4 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] = 81.
Set FIR_LEN = 1 and MUX_DIV[1:0] = 01.
There must be thirteen 32768 Hz 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
Rev. 1.2
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TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
