Renesas R-IN32M3 Series User Manual page 161

R-IN32M3-EC User's Manual 7. Ethernet PHY Function
7.2.3 Cable Diagnostic Function (TDR Function)
The cable diagnostic function (TDR function) is a diagnostic function for detecting the type and location of abnormality
when disconnection or short occurs in the Ethernet cable. This function outputs the pulse to the Ethernet cable and
measures the time of pulse waveform reflected by the cable. This delay time is used to determine the distance of
abnormal and the polarity is used to determine whether it is due to the short or open circuit.
The mechanism is as follows. In the following figures, (1) is the test pulse and (2) is the threshold for detecting the
reflected pulse, and that can be set by the register. When the cable is disconnected (cable end open), the sent pulse will
get back attenuated in the same polarity as shown in Figure 7.2. When the cable is short-circuited (cable end closed), the
sent pulse will get back attenuated in opposite phase as shown in Figure 7.3.
Figure 7.2 Operation when Cable is Disconnected
Figure 7.3 Operation when Cable is Short-Circuited
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Jan. 12, 2021