71M6541F Maxim, 71M6541F Datasheet - Page 101

• Manufacturer Part Number: 71M6541F
• Description: The 71M6541D/71M6541F/71M6541G/71M6542F/71M6542G are Teridian™ 4th-generation single-phase metering SoCs with a 5MHz 8051-compatible MPU core, low-power RTC with digital temperature compensation, flash memory, and LCD driver
• Manufacturer: Maxim

diode and phototransistor implementing a FLAG interface).
UART1. The OPT_TX pin becomes active when the I/O RAM control field OPT_TXE (I/O RAM 0x2456[3:2])
4.9
µWire EEPROMs and other compatible devices should be connected to the DIO pins SEGDIO2/SDCK
and SEGDIO3/SDATA, as described in
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
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
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.
Rev 2
With modulation, an optical emitter can be operated at higher current than nominal, enabling it to
increase the distance along the optical path.
Connecting Three-Wire EEPROMs
Figure
71M654x
SEGDIO3/SDATA
Figure 39: I
SEGDIO2/SDCK
Figure 40: Connections for UART0
71M654x
40.
2.5.9 EEPROM Interface.
TX
RX
2
10 k Ω
C EEPROM Connection
100 pF
10 k Ω
10 k Ω
Figure 41
71M6541D/F/G and 71M6542F/G Data Sheet
EEPROM
SDCK
SDATA
V3P3D
shows the basic connections for
TX
RX
101