Datasheet

FDS 6531/6532 005 Data Sheet 71M6531D/F-71M6532D/F
Rev 2 15
1.3 Digital Computation Engine (CE)
The CE, a dedicated 32-bit signal processor, performs the precision computations necessary to accurately
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 controlled
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 located 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)
Name
Description
0x00
IA
Phase A current
0x01
VA
Phase A voltage
0x02
IB
Phase B current
0x03
VB
Phase B voltage
0x04...0x09
–
Not used
0x0A
TEMP
Temperature
0x0B
VBAT
Battery Voltage
The CE is aided by support hardware to facilitate implementation of equations, pulse counters and
accumulators. This hardware is controlled through I/O RAM locations EQU[2:0] (equation assist), the
DIO_PV and DIO_PW (pulse count assist) bits and PRE_SAMPS[1:0] and SUM_CYCLES[5:0] (accumulation
assist).
PRE_SAMPS[1:0] and SUM_CYCLES[5:0] support a dual level accumulation scheme where the first
accumulator accumulates results from PRE_SAMPS[1:0] samples and the second accumulator accumulates
up to SUM_CYCLES[5:0] of the first accumulator results. The integration time for each energy output is
PRE_SAMPS[1:0] * SUM_CYCLES[5:0]/2520.6 (with MUX_DIV[3:0] = 1). The CE hardware issues the
XFER_BUSY interrupt when the accumulation is complete.