71M6533 Datasheet, PDF (74/132 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6533/G/H and 71M6534/H Data Sheet
FDS_6533_6534_004
71M6533/71M6534
V3P3D
EEPROM
VCC
DIO4
DIO5
DIOn
CLK
10 kΩ ^DI
DO
CS
100 kΩ 100 kΩ
Figure 38: Three-Wire EEPROM Connection
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 Figure 39.
71M6533/71M6534
RX
100 pF 10 kΩ
RX
TX
TX
Figure 39: Connections for UART0
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). Figure 40 shows the basic connections
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.
With modulation, an optical emitter can be operated at higher current than nominal, enabling it to
increase the distance along the optical path.
If operation in BROWNOUT mode is desired, the external components should be connected to V3P3D.
74
Rev 2