DP83826I: The difference between the full-duplex and half-duplex default settings when auto-negotiation is enabled

Hi Atsushi,

Half-Duplex is when only one link partner can talk at a time, like the way humans speak, one talks while the other listens. Full-Duplex means both link partners can speak and listen at the same time.

Did I understand and answer your question?

Regards,

Alvaro

Hi Alvaro-san,

I'm sorry.
My explanation was insufficient.
I understand full-duplex and half-duplex communication methods.

What I'd like to know is what the default settings full-duplex and half-duplex are for.
If auto-negotiation is enabled, full-duplex and half-duplex should be set automatically.

Does it mean that it tries to communicate with the default settings when auto-negotiation fails?

Hi Atsushi,

Auto-negotiation will try to link at the fastest speed and duplex advertised between both PHYs at each end of the link. For 10/100 speeds, the advertisements can be found in Reg 0x4, for 1000 speed, the advertisements can be found in Register 0x9.

For example:

PHY1 <-Ethernet Cable-> PHY2

PHY 1 advertises10/100/1000 Speeds at Full and Half duplex.

PHY 2 advertises only 100 Half duplex

Through the auto-negotiation process, the two PHYs will agree to link up and communicate at 100Mbps half duplex, since that is the only common setting.

Please let me know if I didn't answer your question.

Regards,

Alvaro

Hi Alvaro-san,

Thank you for your reply but my question is not solved.

The default setting I'm referring to is the Full/Half Duplex setting of the Bootstraps option in Basic mode(Table 9-18).

The customer is confused as to whether this bootstrap option should be set to full duplex or half duplex when auto-negotiation is enabled.

If auto-negotiation is enabled, will this setting be ignored?

That is, will it have no effect on communication no matter which setting they use here?

Hi Alvaro-san,

Thanks to your help, I have a better understanding.
However, I still don't fully understand it.

Is my understanding of the following correct?
If that is wrong, please correct it.

- When RX_D0/Strap0 is 1=Half duplex, That is default, only Bit[7, 5] of the ANAR Register (Offset = 4h) will be 1h.

- When RX_D0/Strap0 is 0=Full duplex, only Bit[8, 6] of the ANAR Register (Offset = 4h) will be 1h.

Ideally, we would like to advertise all communication modes, but how can we do this?

Hi Atsushi,

Your understanding is correct. If you want to advertise all modes, please write Reg 0x4 = 0x1E1.

Regards,

Alvaro

Hi Alvaro-san,

You said,
I would recommend the customer strap this into "Full Duplex"

Could you tell me the reason for this?
I'm concerned that by strapping into "Full duplex", "Half duplex" will become unusable with auto-negotiation.