DP83849CVSSLASHNOPB datasheet(42/100 Pages) TI2

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— Receive Window: The receiver can monitor receive

data within a programmable window using the TDR Win-

dow Register (TDR_WIN), address 17h. The window is

controlled by two register values: TDR Start Window, bits

[15:8] of TDR_WIN (17h) and TDR Stop Window, bits

[7:0] of TDR_WIN (17h). The TDR Start Window indi-

cates the first clock to start sampling. The TDR Stop

Window indicates the last clock to sample. By default,

the full window is enabled, with Start set to 0 and Stop

set to 255. The window range is in 8ns clock increments,

so the maximum window size is 2048ns.

5.7.3.4 TDR Results

The TDR function monitors data from the Analog to Digital

Converter (ADC) to detect both peak values and values

above a programmable threshold. It can be programmed

to detect maximum or minimum values. In addition, it

records the time, in 8ns intervals, at which the peak or

threshold value first occurs. The results of a TDR peak and

threshold measurement are available in the TDR Peak

Measurement Register (TDR_PEAK), address 18h and

TDR Threshold Measurement Register (TDR_THR),

address 19h. The threshold measurement may be a more

accurate method of measuring the length for longer cables

to provide a better indication of the start of the received

pulse, rather than the peak value.

Software utilizing the TDR function should implement an

algorithm to send TDR pulses and evaluate results. Multi-

ple runs should be used to best qualify any received pulses

as multiple reflections could exist. In addition, when moni-

toring the transmitting pair, the window feature should be

used to disqualify the transmitted pulse. Multiple runs may

also be used to average the values providing more accu-

rate results.

Actual distance measurements are dependent on the

velocity of propagation of the cable. The delay value is typ-

ically on the order of 4.6 to 4.9 ns/m.

DP83849CVS/NOPB Scheda tecnica(PDF) 42 Page - Texas Instruments