71M6541D Datasheet, PDF (25/166 Pages) Maxim Integrated Products – 0.1% Accuracy Over 2000:1 Current Range Energy Meter ICs

71M6541D/F/G and 71M6542F/G Data Sheet
SUM_SAMPS[12:0] supports an accumulation scheme where the incremental energy values from up to
SUM_SAMPS[12:0] multiplexer frames are added up over one accumulation interval. The integration time
for each energy output is, for example, SUM_SAMPS[12:0]/2520.6 (with MUX_DIV[3:0] = 011, I/O RAM
0x2100[7:4] and FIR_LEN[1:0] = 10, I/O RAM 0x210C[2:1]). CE hardware issues the XFER_BUSY interrupt
when the accumulation is complete.
2.3.3 CE Communication with the MPU
The CE outputs six signals to the MPU: CE_BUSY, XFER_BUSY, XPULSE, YPULSE, WPULSE and
VPULSE. These are connected to the MPU interrupt service. CE_BUSY indicates that the CE is actively
processing data. This signal occurs once every multiplexer frame. XFER_BUSY indicates that the CE is
updating to the output region of the CE RAM, which occurs whenever an accumulation cycle has been
completed. Both, CE_BUSY and XFER_BUSY are cleared when the CE executes a HALT instruction.
XPULSE, YPULSE, VPULSE and WPULSE can be configured to interrupt the MPU and indicate sag
failures, zero crossings of the mains voltage, or other significant events. Additionally, these signals can
be connected directly to DIO pins to provide direct outputs for the CE. Interrupts associated with these
signals always occur on the leading edge (see “External” interrupt source No. 2 in Figure 16).
2.3.4 Meter Equations
The 71M6541D/F/G and 71M6542F/G provide hardware assistance to the CE in order to support various
meter equations. This assistance is controlled through I/O RAM register EQU[2:0] (equation assist). The
Compute Engine (CE) firmware for industrial configurations can implement the equations listed in Table 8.
EQU[2:0] specifies the equation to be used based on the meter configuration and on the number of
phases used for metering.
Table 8: Inputs Selected in Multiplexer Cycles
EQU
Description
Wh and VARh formula
Element 0 Element 1 Element 2
Recommended
Multiplexer
Sequence
0
1-element, 2-W, 1φ with
neutral current sense
VA ∙ IA
VA ∙ IB¹
N/A
1 1-element, 3-W, 1φ
VA(IA-IB)/2
N/A
N/A
IA VA IB¹
IA VA IB
2 † 2-element, 3-W, 3φ Delta
VA ∙ IA
VB ∙ IB
N/A
Note:
1. Optionally, IB may be used to measure neutral current
† 71M6542F/G only
IA VA IB VB
2.3.5 Real-Time Monitor (RTM)
The CE contains a Real-Time Monitor (RTM), which can be programmed to monitor four selectable
XRAM locations at full sample rate. The four monitored locations, as selected by the I/O RAM registers
RTM0[9:8], RTM0[7:0], RTM1[9:8], RTM1[7:0], RTM2[9:8], RTM2[7:0], RTM3[9:8], and RTM3[7:0], are
serially output to the TMUXOUT pin via the digital output multiplexer at the beginning of each CE code
pass. The RTM can be enabled and disabled with control bit RTM_E (I/O RAM 0x2106[1]). The RTM
output is clocked by CKTEST. Each RTM word is clocked out in 35 CKCE cycles (1 CKCE cycle is
equivalent to 203 ns) and contains a leading flag bit. See Figure 10 for the RTM output format. RTM is
low when not in use.
Figure 11 summarizes the timing relationships between the input MUX states, the CE_BUSY signal, and
the RTM serial output stream. In this example, MUX_DIV[3:0] = 4 (I/O RAM 0x2100[7:4]) and
FIR_LEN[1:0] = 10 (I/O RAM 0x210C[1]), (384), resulting in 4 ADC conversions. An ADC conversion
always consumes an integer number of CK32 clocks. Followed by the conversions is a single CK32
cycle.
Figure 11 also shows that the RTM serial data stream begins transmitting at the beginning of state S.
RTM, consisting of 140 CK cycles, always finishes before the next CE code pass starts.