2 functional description, 1 initialization and startup, 2 measurements and signal processing flow – Maxim Integrated 78M6631 User Manual
Page 7: 1 description of measurement equations, Functional description, Initialization and startup, Measurements and signal processing flow, Description of measurement equations, Table 1: measurement equations definitions
UG_6631_078
78M6631 Firmware Description Document
Rev 2
7
2 Functional Description
This section summarizes the functional operation of the 78M6631
firmware. Refer to the IC data sheet
and application notes for more information on terminologies and detailed IC operation.
2.1 Initialization and Startup
Upon power-up, both MPU and Compute Engine (CE) cores start executing the application code from
designated blocks of flash memory. The parameters and defaults are copied from Flash memory into
RAM and accessible (R/W) through the communication interfaces and utilized by the firmware.
After the initialization phase, the firmware starts regular operations and signal processing.
The user can modify any parameters specified as input register, however the modified values are volatile
and will be lost during a power-down or reset. To permanently save the value of the input registers it is
necessary to store them to flash. A section in this document describes which registers can be saved into
flash memory and the relevant command.
2.2 Measurements and Signal Processing Flow
2.2.1 Description of Measurement Equations
The firmware provides the user with continuously updated measurement data. Table 1 lists the basic
measurement equations.
Table 1: Measurement Equations Definitions
Symbol
Parameter
Equation
V
RMS Voltage
V = √∑
v
(t)
2
I
RMS Current
I = √∑
i
(t)
2
P
Active Power
P = ∑
(i
(t) *
v
(t))
Q
Reactive Power
Q = ∑
(i
(t) *
vq
(t))
S
Apparent Power
S = V * I
PF
Power Factor
P/S
PA N/A
Phase Angle
ACOS (P/S)
The integrated AFE and CE function as a data acquisition system, controlled by the MPU. The low-
voltage analog input signals are sampled and stored in CE DRAM where they are processed by the CE.
This firmware utilizes an effective sampling rate of 2521 samples per second. The sampling rate is
referred to each individual channel.
The CE, a dedicated 32-bit signal processor, performs the computations necessary to perform all the
measurements. The CE calculations and processes include:
•
Multiplication of each current sample with its associated voltage sample to obtain the energy per
sample (when multiplied with the constant sample time).
•
Frequency-insensitive delay cancellation on all channels (to compensate for the delay between
samples caused by the multiplexing scheme).
•
90° phase shifter (for VAR calculations).
•
Monitoring of the input signal frequency.
•
Monitoring of the input signal amplitude.
•
Scaling of the processed samples based on calibration coefficients.