DP83869HM: Media converter mode for copper to fiber

Dan Davis

Part Number: DP83869HM
Other Parts Discussed in Thread: DP83869, DP83869EVM,

Howdy All,

I have a few questions about what Aniruddha Khadye previously stated in https://e2e.ti.com/support/interface/f/138/t/791559?tisearch=e2e-sitesearch&keymatch=DP83869HM%2525252520managed%2525252520media%2525252520converter:

1.) "DP83869 needs software access to work in media convertor mode. The software setting is mentioned in the datasheet."

a.) Is this the datasheet statement: "When Media Convertor Mode is enabled then bit [0] of register 0x01EC should be set to 0."?

b.) And if so, what does this bit actually do and why is it needed?

2.) "Also the speed needs to be same on both the copper and the fiber side. The Copper side can auto-negotiate down between 1000M and 100M but the fiber ethernet standard does not support auto-negotiation. So the Fiber speed would need to be changed by software between 1000M and 100M."

a.) If this is so, then why do we have end to end Ethernet communications with the following setup?

100M Copper <> Eval Board #1 (DP83869EVM with strap config only) <> 1000M Fiber SFP <> Fiber Cable <> 1000M Fiber SFP <> Eval Board #2 (DP83869EVM with strap config only) <> 100M Copper

b.) What register needs to be changed in software to configure the Fiber speed to 100M?

Regards,

Dan

over 5 years ago

0 Ross Pimentel over 5 years ago

TI__Mastermind 23675 points

Hi Dan,

The register settings are to enable link forwarding from one port to the other.

If the fiber side drops link, the link on the copper side will be forced off as well.

You need the same speed setting because you will have data corruption if it is not so.

There is no memory so you will see either and under or overflow if one side is 100M and the other is 1G.

Please see register 0xC00 for fiber control register information. This register controls the speed of the fiber port.

0 Dan Davis over 5 years ago in reply to Ross Pimentel

Prodigy 40 points

Howdy Ross,

Thanks for the info.

We are setting the 1G Fiber SFP to 100M.

Now for a few more questions.

Is link forwarding needed?

What would happen if link forwarding is not enabled?

Thanks,

Dan

0 Ross Pimentel over 5 years ago in reply to Dan Davis

TI__Mastermind 23675 points

If you do not enable link forwarding then a link can be present on one side and no link on the other side.

Frames will not make it to the destination but you will see locally that there is link so it makes it more difficult to detect an issue.

0 Dan Davis over 5 years ago in reply to Ross Pimentel

Prodigy 40 points

Howdy Ross,

If that is the case, then what is the difference between Link Loss Pass Thru (configurable through strapping) and Link Forwarding (configurable only through the 0x01EC register)?

Please provide details of the 0x01EC register.

Thanks,

Dan

0 Ross Pimentel over 5 years ago in reply to Dan Davis

TI__Mastermind 23675 points

Hi Dan,

For link pass though (link forwarding) to work in the DP83869HM you need to do both steps: strap for link pass through and configure register 0x1EC.

0 Dan Davis over 4 years ago in reply to Ross Pimentel

Prodigy 40 points

Howdy Ross,

What potential errors may be seen if the 0x1EC register is not configured.

Regards,

Dan

0 Ross Pimentel over 4 years ago in reply to Dan Davis

TI__Mastermind 23675 points

Hi Dan,

If register 0x1EC is not set, link pass through (link forwarding) will not work.

Both must be set to enable the feature.

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DP83869HM: Media converter mode for copper to fiber