Datasheet

71M6543F/71M6543G Data Sheet
116 v2
5.3 CE Interface Description
5.3.1 CE Program
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 and voltage phase measurement. All data computed by the CE
is dependent on the selected meter equation as given by EQU[2:0] (I/O RAM 0x2106[7:5]).
The standard CE program is supplied by Maxim as a data image that can be merged with the MPU
operational code for meter applications. Typically, this CE program covers most applications and does not
need to be modified. Other variations of CE code may be available from Maxim. The description in this
section applies to CE code revision CE43A01A.
5.3.2 CE Data Format
All CE words are 4 bytes. Unless specified otherwise, they are in 32-bit two’s complement format
(-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 0x0000 + 4 x CE_address and by 0x0003 + 4 x CE_address for the least significant byte.
5.3.3 Constants
Constants used in the CE Data Memory tables are:
• Sampling Frequency: F
S
= 32768 Hz/15 = 2184.53 Hz.
• F
0
is the fundamental frequency of the mains phases.
• IMAX is the external rms current corresponding to 250 mV pk at each IADC input.
• VMAX is the external rms voltage corresponding to 250 mV pk at each VADC input.
• N
ACC, the accumulation count for energy measurements is SUM_SAMPS[12:0] (I/O RAM 0x2107[4:0],
0x2108[7:0]). This value also resides in SUM_PRE (CE RAM 0x23) where it is used for phase angle
measurement.
• The duration of the accumulation interval for energy measurements is SUM_SAMPS[12:0] /F
S
.
• X is a gain constant of the pulse generators. Its value is determined by PULSE_FAST and PULSE_SLOW
(see Table 76).
• Voltage LSB = VMAX * 7.879810
-9
V.
• VMAX = 600 V, IMAX = 208 A, and kH = 3.2 Wh/pulse are assumed as default settings.
The system constants IMAX and VMAX are used by the MPU to convert internal digital quantities (as
used by the CE) to external, i.e. metering quantities. Their values are determined by the 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 or MPU interface to external meter input quantities. For example, if a SAG threshold
of 80 V peak is desired at the meter input, the digital value that should be programmed into SAG_THR (CE
RAM 0x24) would be 80 V/SAG_THR
LSB
, where SAG_THR
LSB
is the LSB value in the description of
SAG_THR (Table 77).
The parameters EQU[2:0], CE_E, and SUM_SAMPS[12:0] , essential to the function of the CE are stored in
I/O RAM (see 5.2 for details).