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Quick question on PHY

Paul Calton
Prodigy 20 points

We are developing a product for which we have purchased an TCPIP stack for our processor which included a driver for the on-chip ethernet MAC. One of my colleagues is looking to change the ethernet PHY for a cheaper one when we move from the development kit to our own board.

As I understand it, ethernet PHY are inter-changeable.

i.e. We should be able to replace the ethernet PHY on our circuit with any other using the same interface (MII or RMII) without any issues as the MII/RMII interface provides this compatibility

Can anyone confirm this?

  • 0
    TI__Mastermind 31600 points

    Paul,

    I am afraid I cannot give you a blanket answer since the functionality of individual drivers and the requirements of the operating systems will vary.  In concept, what you say is true, basic Ethernet functionality should be independent of the driver. However, in reality that is not always the case. 

    IEEE specifies basic registers for an Ethernet PHY.  For general purpose applications, this basic register set is often sufficient for packet traffic.  If device specific functionality of the PHY is used, additional registers access(es) must be accounted for by the driver.

    In addition, some basic drivers will perform a device check to confirm the type of PHY being used or the address of the PHY.  If the attached PHY does not match the expectations of the driver, the next step in the process depends the driver.  The driver could continue with basic functionality or it could halt.

    My recommendation would be to delve into the driver itself or work with your processor vendor to get a handle on the how the driver works.  If you find that it can indeed operate independent of the PHY, we can certainly recommend some options from the TI portfolio. 

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 20 points

    Thanks Patrick.

    Ive put in a support ticket with our driver vendor to verify whether they made it to be generic or specific to the PHY on the development board.