Datasheet

DP83849IF
www.ti.com SNOSAX8D –JUNE 2009–REVISED APRIL 2013
8.8.4 TDR Pulse Generator
The TDR implementation can send two types of TDR pulses. The first option is to send 50ns or 100ns link
pulses from the 10Mb Common Driver. The second option is to send pulses from the 100Mb Common
Driver in 8ns increments up to 56ns in width. The 100Mb 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 monitor circuit will still be
activated. This allows sampling of background data to provide a baseline for analysis.
8.8.5 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 8ns 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.
8.8.6 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 10Mb Link pulses from the 10Mb Common Driver or data pulses from the
100Mb Common Driver by enabling TDR 100Mb, 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 Pulse Width is set to 0, then no pulse will be
sent.
Transmit Channel Select:The transmitter can send pulses down either the transmit pair or the receive
pair by enabling bit 13 of TDR_CTRL (16h). Default value is to select the transmit pair.
The following Receive mode controls are available:
Min/Max Mode Select:Bit 7 of TDR_CTRL (16h) controls the TDR Monitor operation. In default mode, the
monitor will detect maximum (positive) values. In Min mode, the monitor will detect minimum
(negative) values.
Receive Channel Select: The receiver can monitor either the transmit pair or the receive pair by enabling
bit 12 of TDR_CTRL (16h). Default value is to select the transmit pair.
Receive Window:The receiver can monitor receive data within a programmable window using the TDR
Window 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 indicates 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.
Copyright © 2009–2013, Texas Instruments Incorporated Design Guidelines 67
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