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Where in clause 28 of the IEEE 802.3 standard does it define what should happen when auto-negotiation fails?

I thought this would be defined but can't find reference to it in the standard?

Thanks.

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28.1.1 Scope states

A device that fails to respond to the FLP Burst sequence by returning only the NLP sequence is treated as a 10BASE-T compatible device.

See Figure 28-17 Receive state diagram. The very first twisted-pair PHY used (normal) link pulses (NLPs) to indicate link availability to its partner. Unless there's an indication of mutually supported better modes, the basic mode is 10BASE-T half duplex.

Figure 28-18 Arbitration state diagram then shows the Autonegotiation phase using fast link pulses (FLPs). Failing that, the link stays at 10BASE-T HDX.

[edit] Capability detection between 100BASE-TX and 10BASE-T (and historically, 100BASE-T4) is defined in 28.2.3.1 Parallel detection function. Its footnote states

When selecting the highest common denominator through the Parallel Detection function, only the halfduplex mode corresponding to the selected PMA may automatically be detected.

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  • Thanks. What in 28-17 denotes that 10BASE-T HDX is the basic mode? Also when I interpret Figure 28-18 it goes back to ABILITY DETECT state continually? What am I getting wrong? Thanks again for the help.
    – Lunch
    Commented Mar 8 at 17:12
  • I added the HDX bit to the answer. Without FLPs, the ABILITY DETECT state isn't ever entered.
    – Zac67 ♦
    Commented Mar 8 at 17:36
  • That's great thanks. I've re-read the clause taking note of your comments and I get it now. I'd misunderstood Parallel Detection function and not noticed Note 2 in 28.2.3.1 until you pointed it out. Thank you ever so much for your help!
    – Lunch
    Commented Mar 11 at 9:09

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