DP83869EVM: Unidirectional fiber communication

LukeR

Prodigy 135 points

Part Number: DP83869EVM
Other Parts Discussed in Thread: DP83869, USB-2-MDIO, MSP430F5529

Tool/software:

Hi, we have a prototype of 1000M media converter using DP83869 chip.

SFP we are using is SFP1G-LX-31-I:

https://www.fs.com/au/products/248907.html

Prototypes (box a and b are exactly the same) are working but only when 'red' fiber is connected:

For our application, unidirectional is required so we can't use that 'red' fiber.

Is there a strap setting for DP83869 that enables us to do unidirectional communication?

ps - our design is based on DP83869 EVM design so straps are all the same:

www.ti.com/.../DP83869EVM

7 months ago

0 Gerome Cacho 7 months ago

TI__Mastermind 39855 points

Hello,

This may be tougher to accomplish as PHY A would need to have link which is part of what RX connection would give (via SD). If the blue line were to ever be disconnected, PHY B would not be able to send a FEF indication.

There is a prior E2E which one of our team member did support:

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1002023/dp83869hm-media-converter-mode-for-1000x-link-up

You may consult this, but otherwise, you may be required to attach the second FX cable. Could there be other ways to "soft" limit the communication to unidirection?

Sincerely,

Gerome

0 LukeR 7 months ago in reply to Gerome Cacho

Prodigy 135 points

Hi Gerome, we're open to replacing DP83869. Any recommendation?

0 Gerome Cacho 7 months ago in reply to LukeR

TI__Mastermind 39855 points

Hello,

This is more of an issue with PHY implementation with FX. With this implementation, one of the PHYs will not understand if there is valid link or not without the RX cable being properly attached. It may be possible to bypass with signal detect on single board, but then the MAC will always believe there is link and send packets out.

Sincerely,
Gerome

0 LukeR 7 months ago in reply to Gerome Cacho

Prodigy 135 points

Hi Gerome, would USB-2-MDIO enable us to access registers of DP83869 in our prototype board?

0 Gerome Cacho 7 months ago in reply to LukeR

TI__Mastermind 39855 points

Hello,

USB2MDIO would help, but it would require a flashed MSP430F5529 with appropriate connections. If that is available on-board (similar implementation to EVM), or a launchpad is available, this would be feasible.

Sincerely,

Gerome

0 LukeR 7 months ago in reply to Gerome Cacho

Prodigy 135 points

Update: we were able to read registers using USB-2-MDIO tool. we just can't get the loopback setting to work.

Anyway, here is our current hardware setup:

Is it worth attempting this hardware modification?

0 Gerome Cacho 7 months ago in reply to LukeR

TI__Mastermind 39855 points

Hello,

Which loopback are you looking to implement? Is it copper side reverse loopback? If so, please ensure that Reg 0x16[5:2] = 0x8.

Sincerely,

Gerome

0 LukeR 7 months ago in reply to Gerome Cacho

Prodigy 135 points

We just want a unidirectional transport from SFP TX to RX of another SFP. Please see original diagram above. We don't want that 'red' fiber connected.

DP83869 is configured in 1000Base-T to 1000Base-X mode.

0 Gerome Cacho 7 months ago in reply to LukeR

TI__Mastermind 39855 points

Hello,

Without the red connection, the DUT may not understand that it is linked in FX and thus may not convert the copper signal to fiber.

Again, which loopback are you having issues with?

Sincerely,

Gerome

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DP83869EVM: Unidirectional fiber communication