DP83869HM: FX_LPABL Register reserved pins

Hi Konstantinos,

Thank you for getting in touch with us.

Fiber modes don't have speed auto-negotiation in which the link partner advertises the speed. So there is no way for the DUT (DP83869 here) to know the speed of the link partner.

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Regards,
Gokul.

Hi Gokul,

Thank you for your quick response.

I don't think it's the copper side connected speed but it's the partner's fiber side speed.

Considering that a fiber Rx (Device B Tx) is connected to Device A and a fiber Rx (Device A Tx)is connected to Device B it's not strange to retrieve the partners fiber speed. So, if there is a speed mismatch between the fibers, it's seems i can see it by reading those 2 bits.

Is this make sense?

I tried in multiple DP83869HM ICs and those 2 bits are giving me this information as it is described in my previous post.

Thank you.

Konstantinos

Hi Konstantinos,

Can you please let me know what is the Fiber link partner used with DP83869?

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Regards,
Gokul.

Hi Gokul,

Please, see image below.

Device A and device B are the same product.

So Device A is able to read the speed of device B and vice versa, by reading bits 10 and 11 of FX_LPABL register. 

Is there a proper way that Device A or Device B understands that there is speed mismatch?

Thank you.

Konstantinos 

Hi Konstantinos,

Can you please confirm which bits you think are giving the indication? The first message says 10-9, but the last message says 11-10.

Also, in the first message, you mentioned the bits reading 00 for 10Mbps Fiber. The DP83869HM doesn't have support for 10M Fiber. Were you using different fiber link partner during this observation?

Can you please let me know the following information?

1. Please confirm that you are reading register 0xC05?
2. How are the 869HM devices configured in Fiber mode? Is it through straps or register configuration? If register configuration, please let me know the register values programmed.
3. When you are testing the register bits with 100M Fiber link partner, can you please let me know what is speed configured for the DUT (Device A on which register bits are read)?
4. Please provide the whole register read value with 100M and 1G Fiber link partner.

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Regards,
Gokul.

Hi Gokul,

The block diagram above is representing our application and the configuration. The H/W strap configuration is shown in the block diagram.

Our mode is copper to SGMII.

I don't know if the fibre side can work at 10Mbps or not but I can confirm that if Laptop and Desktop PC are connected to copper side at 10Mbps they can communicate. I have tried all the speeds 1000Mbps to 1000Mbps, 100Mbps to 100Mbps and 10Mbps to 10Mbps and it works.

Yes, I read Register 0xC05. My first post is mentioning bits 9 and 10 by mistake. The correct pins are 10 and 11.

Please see below examples.

I remind you that I don't know the fiber link speed. I know the copper side speed. I assume that in order to have communication Fiber speed must be equal to copper side speed otherwise I will not have communication. 

In the examples below I have communication between Laptop and Desktop PC only when Device A and Device B copper side link is 10Mbps. In the other 2 examples I don't have communication because there is speed mismatch.

Thank you,

Konstantinos

Hi Gokul,

Is the functionality of those pins going to be documented in an updated version of the datasheet?

Otherwise how can I validate my product if it is based on a non documented functionality?

Thank you.

Konstantinos