71M6543G Maxim, 71M6543G Datasheet - Page 95

• Manufacturer Part Number: 71M6543G
• Description: The 71M6543F/71M6543H are Teridian's 4th-generation polyphase metering system-on-chips (SoCs) with a 5MHz, 8051-compatible MPU core, low-power real-time clock (RTC) with digital temperature compensation, flash memory, and LCD driver
• Manufacturer: Maxim

set to 00.
for UART1. The OPT_TX pin becomes active when the control field OPT_TXE (I/O RAM 0x2456[3:2]) is
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.
If operation in BRN mode is desired, the external components should be connected to V3P3D. However,
it is recommended to limit the current to a few mA.
4.10 Connecting the Reset Pin
Even though a functional meter does not necessarily need a reset switch, it is useful to have a reset
pushbutton for prototyping as shown in
V3P3SYS (functional in MSN mode only), V3P3D (MSN and BRN modes), or VBAT (all modes, if a battery is
present), or from a combination of these sources, depending on the application.
Since the 71M6543 generates its own power-on reset, a reset button or circuitry, as shown in
only required for test units and prototypes.
v1.2
increase the distance along the optical path.
With modulation, an optical emitter can be operated at higher current than nominal, enabling it to
For a production meter, the RESET pin should be protected by the by the external components
shown in
to the IC.
Figure
36, right side. R1 should be in the range of 100Ω and mounted as closely as possible
71M6543
© 2008–2011 Teridian Semiconductor Corporation
Figure 35: Connection for Optical Components
OPT_RX
OPT_TX
Figure
100 pF
36, left side. The RESET signal may be sourced from
10 kΩ
R
2
71M6543F/H and 71M6543G/GH Data Sheet
V3P3SYS
R
LED
Phototransistor
1
V3P3SYS
Figure
36, is
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