71M6533G Maxim, 71M6533G Datasheet - Page 74

• Manufacturer Part Number: 71M6533G
• Description: The Teridian™ 71M6533 and 71M6534 are third-generation polyphase metering systems-on-chips (SoCs) with a 10MHz 8051-compatible MPU core, low-power RTC, flash, and LCD driver
• Manufacturer: Maxim

4.5 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
4.6 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).
for UART1. The OPT_TX pin becomes active when the OPT_TXE[1:0] I/O RAM field is set to 00.
The polarity of the OPT_TX and OPT_RX pins can be inverted with the configuration bits, OPT_TXINV
and OPT_RXINV, respectively.
The OPT_TX output may be modulated at 38 kHz when system power is present. Modulation is not
available in BROWNOUT mode. The OPT_TXMOD bit enables modulation. The duty cycle is controlled
by OPT_FDC[1:0], 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 and may need an
analog filter when receiving modulated optical signals.
If operation in BROWNOUT mode is desired, the external components should be connected to V3P3D.
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With modulation, an optical emitter can be operated at higher current than nominal, enabling it to
increase the distance along the optical path.
71M6533/71M6534
Figure
71M6533/71M6534
Figure 38: Three-Wire EEPROM Connection
39.
V3P3D
DIO4
DIO5
DIOn
Figure 39: Connections for UART0
TX
RX
100 kΩ
100 pF
100 kΩ
10 k Ω
10 k Ω
Figure 40
VCC
CLK
DO
CS
DI
EEPROM
TX
RX
shows the basic connections
Rev 2