71M6543F Datasheet, PDF (27/157 Pages) Maxim Integrated Products – Selectable Gain of 1 or 8 for One Current Energy Meter ICs Metrology Compensation

71M6543F/H and 71M6543G/GH Data Sheet
A common use of the zero-crossing pulses is to generate interrupts in order to drive real-time clock
software in places where the mains frequency is sufficiently accurate to do so and also to adjust for
crystal aging. A common use for the SAG pulse is to generate an interrupt that alerts the MPU when mains
power is about to fail, so that the MPU code can store accumulated energy and other data to EEPROM
before the V3P3SYS supply voltage actually drops.
2.3.6.1 XPULSE and YPULSE
Pulses generated by the CE may be exported to the XPULSE and YPULSE pulse output pins. Pins
SEGDIO6 and SEGDIO7 are used for these pulses, respectively. Generally, the XPULSE and YPULSE
outputs can be updated once on each pass of the CE code.
See 5.4 CE Interface Description on page 120 for details.
2.3.6.2 VPULSE and WPULSE
Referring to Figure 9, during each CE code pass the hardware stores exported WPULSE and VPULSE sign
bits in an 8-bit FIFO and outputs them at a specified interval. This permits the CE code to calculate the
VPULSE and WPULSE outputs at the beginning of its code pass and to rely on hardware to spread them
over the multiplexer frame. As seen in Figure 9, the FIFO is reset at the beginning of each multiplexer
frame. As also seen in Figure 9, the I/O RAM register PLS_INTERVAL[7:0] (I/O RAM 0x210B[7:0]) controls
the delay to the first pulse update and the interval between subsequent updates. The LSB of the
PLS_INTERVAL[7:0] register is equivalent to 4 CK_FIR cycles (CK_FIR is typically 4.9152MHz if PLL_FAST=1
and ADC_DIV=0, but other CK_FIR frequencies are possible; see the ADC_DIV definition in Table 71.) If
PLS_INTERVAL[7:0]=0, the FIFO is deactivated and the pulse outputs are updated immediately.
The MUX frame duration in units of CK_FIR clock cycles is given by:
If PLL_FAST=1:
MUX frame duration in CK_FIR cycles = [1 + (FIR_LEN+1) * (ADC_DIV+1) * (MUX_DIV)] * [150 / (ADC_DIV+1)]
If PLL_FAST=0:
MUX frame duration in CK_FIR cycles = [3 + 3*(FIR_LEN+1) * (ADC_DIV+1) * (MUX_DIV)] * [48 / (ADC_DIV+1)]
PLS_INTERVAL[7:0] in units of CK_FIR clock cycles is calculated by:
PLS_INTERVAL[7:0] = floor ( Mux frame duration in CK_FIR cycles / CE pulse updates per Mux frame / 4 )
Since the FIFO resets at the beginning of each multiplexer frame, the user must specify
PLS_INTERVAL[7:0] so that all of the possible pulse updates occurring in one CE execution are output
before the multiplexer frame completes. For instance, the 71M6543 CE code outputs six updates per
multiplexer interval, and if the multiplexer interval is 1950 CK_FIR clock cycles long, the ideal value for
the interval is 1950/6/4 = 81.25. However, if PLS_INTERVAL[7:0] = 82, the sixth output occurs too late and
would be lost. In this case, the proper value for PLS_INTERVAL[7:0] is 81 (i.e., round down the result).
Since one LSB of PLS_INTERVAL[7:0] is equal to 4 CK_FIR clock cycles, the pulse time interval TI in units of
CK_FIR clock cycles is:
TI = 4*PLS_INTERVAL[7:0]
If the FIFO is enabled (i.e., PLS_INTERVAL[7:0] ≠ 0), hardware also provides a maximum pulse width feature
in control register PLS_MAXWIDTH[7:0] (I/O RAM 0x210A) . By default, WPULSE and VPULSE are negative
pulses (i.e., low level pulses, designed to sink current through an LED). PLS_MAXWIDTH[7:0] determines the
maximum negative pulse width T_MAX in units of CK_FIR clock cycles based on the pulse interval T_I
according to the formula:
T_MAX = (2 * PLS_MAXWIDTH[7:0] + 1) * T_I
If PLS_MAXWIDTH = 255 or PLS_INTERVAL=0, no pulse width checking is performed, and the pulses
default to 50% duty cycle.
The polarity of the pulses may be inverted with the control bit PLS_INV (I/O RAM 0x210C[0]). When
PLS_INV is set, the pulses are active high. The default value for PLS_INV is zero, which selects active low
pulses.
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