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LMH1297: Using LMH1297 with mixed SDI and MADI formats

Josh Duncan
Prodigy 10 points
Part Number: LMH1297

Tool/software:

Hi there,

This application note (https://www.ti.com/lit/an/snla299/snla299.pdf) details a use case where the LMH1297 can be used as an SDI bidirectional IO as well as a MADI cable driver simultaneously.

The application note provides no details on how this configuration is supported, and which register bits need to be set to support this. It is my understanding that the SDI_OUT cable driver cannot be used as a standalone cable driver when SDI_IO is used in EQ mode, however this is contradicted by two of the four modes detailed in that application note.

Can anyone elaborate further on how this shared SDI/MADI mode works?

Thanks

  • 0
    TI__Genius 9209 points

    Hi Josh,

    When SDI_IO is in EQ mode, the second 75-Ω driver (SDI_OUT) can be used as a loop-through output. It is possible to use SDI_IO as a regular SDI bidirectional IO and SDI_OUT as a MADI output (when SDI_OUT is enabled).

    Best,

    Nick

  • 0 in reply to Nick Peabody
    Prodigy 10 points

    Thanks for the quick reply Nick.

    Where would the MADI signal on the SDI_OUT come from? If SDI_OUT is a loop-through of SDI_IO, would it not just output a copy of the SDI signal at the input? Is it possible to take a MADI signal in on IN+/- and output it via SDI_OUT when SDI_IO is in EQ mode?

    Cheers,

    Josh

  • 0 in reply to Josh Duncan
    TI__Mastermind 36043 points

    Hi Josh,

    Nick will get back to you with a reply tomorrow.  Thanks for your patience.

    Thanks,

    Drew

  • 0 in reply to Josh Duncan
    TI__Genius 9209 points

    Hi Josh,

    SDI_OUT is not just a loop-through of SDI_IO it is also a loop through of IN0+/-.

    See the image above for a block diagram. When SDI_OUT is enabled, the data will loop-through from either SDI_IO in EQ mode or IN0 depending on which is enabled and receiving data. You can only have one input at a time.

    You could have SDI and MADI simultaneously with SDI on SDI_IO and MADI on IN0+/- by disabling one input at a time.

    Best,

    Nick