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TMS320F28388D: Pin29 of DP83822 on TMDSCNCD28388D

Brian Wang0
Expert 5390 points
Part Number: TMS320F28388D
Other Parts Discussed in Thread: TMDSCNCD28388D

Hi team,

I am supporting my customer on their design with F28388 and 2 DP83822.

We noticed on TMDSCNCD28388D schematic, the 29 pin of one DP83822 is pulled up while the other one is pulled down.

Refer to DP83822 datasheet, it noted the this pin should be PU. Since we are not expert on PHY, we would like to know why we are implementing PIN 29 on two PHYs in different way?

Regards,

Brian 

  • 0
    TI__Expert 5391 points

    Hi Brian,

    Pin no 29 of DP83822 PHY is also used to program the PHY address during power up of PHY. 

    Datasheet of PHY also mentions this 

    "PHY_AD[0] (LSB of the address) is multiplexed with COL on pin 29, and is pulled up. If no external pullup or pulldown is present, the default PHY address is 0x01"

    Hence we do an explicit Pull Up in one and pull down in other to assign an address of 0 and 1 to differentiate the PHYs (over MDIO interface).

    Regards,

    Sudharsanan