71M6541D Datasheet, PDF (101/166 Pages) Maxim Integrated Products – 0.1% Accuracy Over 2000:1 Current Range Energy Meter ICs

71M6541D/F/G and 71M6542F/G Data Sheet
10 kΩ
SEGDIO2/SDCK
SEGDIO3/SDATA
71M654x
V3P3D
10 kΩ
EEPROM
SDCK
SDATA
Figure 39: I²C EEPROM Connection
4.9 Connecting Three-Wire EEPROMs
µWire EEPROMs and other compatible devices should be connected to the DIO pins SEGDIO2/SDCK
and SEGDIO3/SDATA, as described in 2.5.9 EEPROM Interface.
4.10 UART0 (TX/RX)
The UART0 RX pin should be pulled down by a 10 kΩ resistor and additionally protected by a 100 pF
ceramic capacitor, as shown in Figure 40.
71M654x
RX
100 pF 10 kΩ
RX
TX
TX
Figure 40: Connections for UART0
4.11 Optical Interface (UART1)
The OPT_TX and OPT_RX pins can be used for a regular serial interface (by connecting a RS_232
transceiver for example), or they can be used to directly operate optical components (for example, an infrared
diode and phototransistor implementing a FLAG interface). Figure 41 shows the basic connections for
UART1. The OPT_TX pin becomes active when the I/O RAM control field OPT_TXE (I/O RAM 0x2456[3:2])
is set to 00.
The polarity of the OPT_TX and OPT_RX pins can be inverted with the configuration bits, OPT_TXINV
(I/O RAM 0x2456[0]) and OPT_RXINV (I/O RAM 0x2457[1]), respectively.
The OPT_TX output may be modulated at 38 kHz when system power is present. Modulation is not
available in BRN mode. The OPT_TXMOD bit (I/O RAM 0x2456[1]) enables modulation. The duty cycle is
controlled by OPT_FDC[1:0] (I/O RAM 0x2457[5:4]), which can select 50%, 25%, 12.5%, and 6.25% duty
cycle. A 6.25% duty cycle means OPT_TX is low for 6.25% of the period. The OPT_RX pin uses digital
signal thresholds. It may need an analog filter when receiving modulated optical signals.
With modulation, an optical emitter can be operated at higher current than nominal, enabling it to
increase the distance along the optical path.