71M6511 Maxim, 71M6511 Datasheet - Page 83

• Manufacturer Part Number: 71M6511
• Description: The 71M6511 and 71M6511H are highly integrated SoCs with an MPU core, RTC, flash, and LCD driver
• Manufacturer: Maxim

Optical Interface
The pins OPT_TX and OPT_RX can be used for a regular serial interface, e.g. by connecting a RS_232 transceiver, or they
can be used to directly operate optical components, e.g. an infrared diode and phototransistor implementing a FLAG interface.
Figure 35 shows the basic connections. The OPT_TX pin becomes active when the I/O RAM register OPT_TXDIS is set to 0.
Connecting V1 and Reset Pins
A voltage divider should be used to establish a safe range for V1 when the meter is in mission mode (V1 must be lower than
2.9V in all cases in order to keep the hardware watchdog timer enabled). For proper debugging or loading code into the
71M6511 mounted on a PCB, it is necessary to have a provision like the header shown above R1 in Figure 36. A shorting
jumper on this header pulls V1 up to V3P3, disabling the hardware watchdog timer. C1 helps suppressing ESD.
Even though a functional meter will not necessarily need a reset switch, it is useful to have a reset pushbutton for prototyping.
When a circuit is used in an EMI environment, the RESETZ pin should be supported by the external components shown in
Figure 37. R
be mounted as close as possible to the IC. In cases where the trace from the pushbutton switch to the RESETZ pin poses a
problem, R
Page: 83 of 98
A Maxim Integrated Products Brand
2
can be removed.
1
should be in the range of 200Ω, R
V
V
71M6511
71M6511
in
in
OPT_RX
OPT_RX
OPT_TX
OPT_TX
Figure 35: Connection for Optical Components
© 2005–2010 Teridian Semiconductor Corporation
Figure 36: Voltage Divider for V1
2
R
R
100pF
100pF
should be around 10Ω. The capacitor C
1
1
R
R
2
2
100kΩ
100kΩ
R
R
2
2
Single-Phase Energy Meter IC
10kΩ
10kΩ
R
R
3
3
100pF
100pF
R
R
Phototransistor
Phototransistor
LED
LED
1
1
V3P3
V3P3
C
C
71M6511/71M6511H
1
1
DATA SHEET
V3P3
V3P3
V1
V1
1
should be 1nF. R1 and C1 should
NOVEMBER 2010
V2.7