71M6531D Datasheet, PDF (15/115 Pages) Teridian Semiconductor Corporation – Energy Meter IC

FDS 6531/6532 005
Data Sheet 71M6531D/F-71M6532D/F
1.3 Digital Computation Engine (CE)
The CE, a dedicated 32-bit signal processor, performs the precision computations necessary to accurate-
ly measure energy. 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 four channels (to compensate for the delay between
samples caused by the multiplexing scheme).
• 90° phase shifter (for VAR calculations).
• Pulse generation.
• Monitoring of the input signal frequency (for frequency and phase information).
• Monitoring of the input signal amplitude (for sag detection).
• Scaling of the processed samples based on calibration coefficients.
• Scaling of all samples based on temperature compensation information (71M6532D/F only).
The CE program resides in flash memory. Common access to flash memory by CE and MPU is con-
trolled by a memory share circuit. Each CE instruction word is two bytes long. Allocated flash space for
the CE program cannot exceed 4096 16-bit words (8 KB). The CE program counter begins a pass
through the CE code each time multiplexer state 0 begins. The code pass ends when a HALT instruction
is executed. For proper operation, the code pass must be completed before the multiplexer cycle ends
(see Section 2.2 System Timing Summary).
The CE program must begin on a 1-KB boundary of the flash address. The I/O RAM register
CE_LCTN[7:0] defines which 1-KB boundary contains the CE code. Thus, the first CE instruction is lo-
cated at 1024*CE_LCTN[7:0].
The CE can access up to 4 KB of data RAM (XRAM), or 1024 32-bit data words, starting at RAM address
0x0000.
The XRAM can be accessed by the FIR filter block, the RTM circuit, the CE, and the MPU. Assigned time
slots are reserved for FIR, and MPU, respectively, to prevent bus contention for XRAM data access.
The MPU can read and write the XRAM as the primary means of data communication between the two
processors. Table 4 shows the CE addresses in XRAM allocated to analog inputs from the AFE.
Table 4: XRAM Locations for ADC Results
Address (HEX)
0x00
0x01
0x02
0x03
0x04...0x09
0x0A
0x0B
Name
IA
VA
IB
VB
–
TEMP
VBAT
Description
Phase A current
Phase A voltage
Phase B current
Phase B voltage
Not used
Temperature
Battery Voltage
The CE is aided by support hardware to facilitate implementation of equations, pulse counters and accu-
mulators. This hardware is controlled through I/O RAM locations EQU (equation assist), DIO_PV and
DIO_PW (pulse count assist) and PRE_SAMPS and SUM_CYCLES (accumulation assist).
PRE_SAMPS and SUM_CYCLES support a dual level accumulation scheme where the first accumulator
accumulates results from PRE_SAMPS samples and the second accumulator accumulates up to
SUM_CYCLES of the first accumulator results. The integration time for each energy output is PRE_SAMPS
* SUM_CYCLES/2520.6 (with MUX_DIV = 1). The CE hardware issues the XFER_BUSY interrupt when
the accumulation is complete.
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