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71M6513/71M6513H Demo Board User’s Manual
Page: 59 of 112
©
2005-2006 TERIDIAN Semiconductor Corporation
Revision 5.6
J12 on the D6513T3C1 Demo Boards has all the provisions for connecting the IR LED and photo-transistor (see
Figure 2-15). Depending on the required LED current, R79 may have to be scaled. Similarly, R84 may be scaled
or removed, depending on the current generated by the photo-transistor.
R79
100
GND
V3P3
OPT_TX
R84
47K
OPT_TX_OUT
1
2
3
4
5
J12
HDR5x1
OPTICAL I/F
OPT_RX
GND
Figure 2-15: Optical Port Circuitry on the D6513T3C1 Demo Board
2.4.7 CONNECTING THE RX PIN
Due to unique circuitry on the RX input, its behavior is slightly different from the other digital inputs of the 651X
family of metering ICs.
The Rx pin (serial port receive pin) of the 71M6513/6513H is internally clamped to the V3P3 supply as shown in
Figure 2-16. This means, the voltage of signals applied to this pin will be clamped to V3P3D + 0.6V, i.e.
nominally 3.9V. Note that this clamp voltage exceeds the 3.6V Absolute Maximum Rating of the RX input.
Inputs above 1.6V (V
IL
) are guaranteed to be recognized as logic 1. Inputs below 0.8V (V
IL
) are guaranteed to
be recognized as logic 0. Input voltages between 0.8V and 1.6V must be avoided.
Figure 2-16: Internal Diode Clamp on the RX Pin
To serial receiver
RX
V3P3
71M6513
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