Tuesday, April 25, 2017

Auto-Negotiation Testing Procedure

The purpose of this guide is to determine a device’s auto-negotiation abilities using an oscilloscope.

Equipment used in this test:
  1. RIGOL DS1054Z - 4 Channel Oscilloscope
  2. Siemon MODAPT- 8pin “banjo”

Connecting the Oscilloscope
  1. De-energize the device under test.
  2. Connect a copper patch cable (Cat5e or better) to the device under test.
  3. Using a “banjo” as shown above connect probe to pin 1 and ground to pin 2.
    1. If no bajo is available a patch cable with a standard RJ-45 Male connector on one end terminated using TIA-568B can be used. Strip back the other end of the cable exposing the 4 pairs of conductors. Strip back 1” of insulation on the wh/orange and orange conductors. Connect the probe to the wh/orange and ground clip to the orange conductor.
  4. Energize the device under test

Setting up the Oscilloscope

Initial settings:
Trigger-2V (auto on most scopes will work best)
This will show the Auto-negotiation pulses also known as Fast Link Pules (FLP). This is shown in the screenshot above.

Analyzing FLP
After capturing a set of FLP’s, change the settings on the oscilloscope.

Note the 17 clock pulses. The time between each clock pulse is 125µs +/-14µs. These will be accompanied by 16 data pulses. These 16 data pulses represent one 16-bit word. The presence of the data bit represents a binary 1. The lack of data pulse
represents a binary 0.  We can analyze the data bits to see what the device under test is advertising as it’s abilities. The screenshot above represents a device that is capable of 100Mbs Full-duplex.

Auto-negotiation uses the greatest common denominator between each side of the link to establish the best possible connection.

If you have any questions, please contact:

Shawn White - Shawn@teamtech1.com

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