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Can DP83848M work just using strap pins?

Jimmy Chou1
Prodigy 10 points
Other Parts Discussed in Thread: DP83848M

Hi Sir:

   We just set DP83848M strap pins for MII mode, and we did not use MDC/MDIO (pull up MDIO by a 1.5KOhm). All my strap pins use default value.

But it didn't work. RX_CLK got a 25MHz output, RX_DV & RX_D[3:0] always low. Should I write some registers by MDC/MDIO? Which registers need to be written in?

Thanks

Jimmy

  • 0
    TI__Mastermind 31600 points

    Jimmy,

    The DP83848 is designed to allow configuration for most functionality using straps.  For many applications, configuration using just strap pins is sufficient.

    What board are you using, a TI EVM or a board of your own design or something else?  What is connected to the DP83848 MII pins?  What is the link partner on the other end of the CAT-5 cable?

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 10 points

    Hello Patrick:

       Our application is back plane connection. We removed CAT-5 cable & transformer commecting DP83848 and AX11015 (ASIX single chip Microcontroller Fast Ethernet MAC/PHY) with PCB traces. We make sure impedance is matched and couple capacitors are mounted.

       We read DP83848 registers by MDC/MDIO. We found both PHYs already link but RX_DV & RXD[3:0] always "Low" during we wer sendng data. I show the registers read from DP83848. Could you please check that for us? and tell me what my mistake is.

    Thanks

    Jimmy

    REG(0x0010)(0x4000)

    REG(0x0006)(0x0005)

    REG(0x0005)(0x45e1)

    REG(0x0006)(0x0007)

    REG(0x0007)(0x2801)

    REG(0x0006)(0x0005)

    REG(0x0010)(0x4004)

    REG(0x0012)(0x0800)

    REG(0x0012)(0x0000)

    REG(0x0001)(0x7869)

    REG(0x0010)(0x4015)

    REG(0x0012)(0x2400)

    REG(0x0001)(0x786d)

    REG(0x0010)(0x4615)

    REG(0x0012)(0x0000)