LXT9784 Octal 10/100
Transceiver Hardware Integrity
Function Overview
Application Note
January 2001
Order Number:
249188-001
As of January 15, 2001, this document replaces the Level One document known as AN123.
Application Note
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Application Note
3
LXT9784 Octal 10/100 Transceiver Hardware Integrity Function Overview
Contents
1.0
Connection Types
...................................................................................................... 5
1.1
Isolating Cabling Problems.................................................................................... 5
2.0
Transmission Lines and Return Wave Theory
............................................... 7
2.1
Cable Terminations and Return Loss.................................................................... 7
2.2
Checking for Cable Length.................................................................................... 9
2.2.1
Accuracy of Measurement........................................................................ 9
3.0
Hardware Integrity Management Register
..................................................... 10
4.0
Hardware Integrity Test Function
...................................................................... 11
5.0
Hardware Integrity Test Program
...................................................................... 12
Figures
1
Forward and Return Waves .................................................................................. 8
2
HWI Test Algorithm ............................................................................................. 11
Tables
1
Typical CAT5 Return Loss .................................................................................... 7
2
Tx and Rx Return Loss.......................................................................................... 8
3
Register 29 (1D Hex) Hardware Integrity Control Register Bit Assignments ...... 10
4
Register 29 (1D Hex) Hardware Integrity Control Register Bit Definitions .......... 10
LXT9784 Octal 10/100 Transceiver Hardware Integrity Function Overview
Application Note
5
1.0
Connection Types
Cabling problems can be the cause of significant network downtime. With today's network
manager more concerned about "Total Cost of Ownership", features that can help solve cabling
problems provide valuable benefits. The Hardware Integrity (HWI) function incorporated into the
LXT9784 is one such feature.
The Hardware Integrity function uses transmission line theory to measure the arrival time and
electrical characteristics of the wave reflected back from an incident test wave launched on the
media. With these measurements, opens, shorts, and degraded cable quality can be located along
the wire, and lead the network manager to the location of the problem.
This document provides a theoretical overview of the HWI function implemented in the LXT9784.
1.1
Isolating Cabling Problems
When looking at cabling plant installation, it consists of many different pieces:
The cable connection from the PC to the wall plate
The wall plate
The cables from the wall plate to the wiring closet
The wiring closet patch panels
The RJ45 connectors everywhere
The patch cables to the network hub.
Hand-held CAT-5 UTP cable testers are frequently used to isolate cabling problems. A typical
cable test involves connecting one end of the cable to the tester, and connecting a remote node
terminator or loopback module to the other end.
Then the tester performs cable link analysis and is able to detect the following conditions:
Short when two or more lines are short-circuited together.
Open Lack of continuity between pins at both ends of the cable.
Crossed pair When a pair is connected to different pins at each end (i.e. Pair 1 is connected
to pins 1&2 at one end and pins 3&6 at the other).
Reversed pair when two lines in a pair are connected to opposite pins at each end of the
cable (i.e. the line on pin 1 is connected to pin 2 at the other end, the line on pin 2 is connected
to pin 1), also called polarity reversal.
Distance In addition it is able to locate the distance to an open or short and to measure cable
length.
The tester uses a technique called TDR (Time Domain Reflection) based on transmission line
theory. This technique transmits a pulse down the cable, and measures the elapsed time until it
receives a reflection from the far end of the cable.
The LXT9784 10/100 Ethernet Octal PHY device uses a similar approach. Each of the device ports
has the capability to independently detect and report cabling problems via the MII management
interface (MDIO) - without the need to unplug cables, connect test equipment or install a loopback
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