Datasheet

DP83640
SNOSAY8E –SEPTEMBER 2007–REVISED APRIL 2013 www.ti.com
2. Write 8000 to LQMR to enable the Link Quality Monitor (if not already enabled).
5.10.3 TDR Cable Diagnostics
The DP83640 implements a Time Domain Reflectometry (TDR) method of cable length measurement and
evaluation which can be used to evaluate a connected twisted pair cable. The TDR implementation
involves sending a pulse out on either the Transmit or Receive conductor pair and observing the results
on either pair. By observing the types and strength of reflections on each pair, software can determine the
following:
• Cable short
• Cable open
• Distance to fault
• Identify which pair has a fault
• Pair skew
The TDR cable diagnostics works best in certain conditions. For example, an unterminated cable provides
a good reflection for measuring cable length, while a cable with an ideal termination to an unpowered
partner may provide no reflection at all.
5.10.4 TDR Pulse Generator
The TDR implementation can send two types of TDR pulses. The first option is to send 50 ns or 100 ns
link pulses from the 10 Mb Common Driver. The second option is to send pulses from the 100 Mb
Common Driver in 8 ns increments up to 56 ns in width. The 100 Mb pulses will alternate between positive
and negative pulses. The shorter pulses provide better ability to measure short cable lengths, especially
since they will limit overlap between the transmitted pulse and a reflected pulse. The longer pulses may
provide better measurements of long cable lengths.
In addition, if the pulse width is programmed to 0, no pulse will be sent, but the monitor circuit will still be
activated. This allows sampling of background data to provide a baseline for analysis.
5.10.5 TDR Pulse Monitor
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 8 ns intervals, at which the peak or threshold value first occurs.
The TDR monitor implements a timer that starts when the pulse is transmitted. A window may be enabled
to qualify incoming data to look for response only in a desired range. This is especially useful for
eliminating the transmitted pulse, but also may be used to look for multiple reflections.
5.10.6 TDR Control Interface
The TDR Control Interface is implemented in the Link Diagnostics Registers - Page 2 through TDR
Control (TDR_CTRL), address 16h and TDR Window (TDR_WIN), address 17h. The following basic
controls are:
• TDR Enable: Enable bit 15 of TDR_CTRL (16h) to allow the TDR function. This bypasses normal
operation and gives control of the CD10 and CD100 block to the TDR function.
• TDR Send Pulse: Enable bit 11 of TDR_CTRL (16h) to send the TDR pulse and starts the TDR
Monitor
The following transmit mode controls are available:
• Transmit Mode: Enables use of 10 Mb Link pulses from the 10 Mb Common Driver or data pulses
from the 100 Mb Common Driver by enabling TDR_100 Mb, bit 14 of TDR_CRTL (16h).
• Transmit Pulse Width: Bits [10:8] of TDR_CTRL (16h) allows sending of 0 to 7 clock width pulses.
Actual pulses are dependent on the transmit mode. If the pulse width is set to 0, then no pulse will be
sent.
50 Configuration Copyright © 2007–2013, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Links: DP83640