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DP83TC811R-Q1: Why does plugging/unplugging the network cable on the dp83tc811r cause changes in the AUTO_PHY register?

Annie Liu
Genius 10295 points
Part Number: DP83TC811R-Q1


Hi Team,

Customer has below question need you help.

Problem Description:

Perform the following operations to read AUTO_PHY

1. When the network cable is unplugged, the value of AUTO_PHY is 0x5a.

2. After plugging the network cable, the value of AUTO_PHY is 0x1a.

3. After unplugging the network cable, the value of AUTO_PHY is 0x1a, and does not return to 0x5a.

4. The software sets the value of the register AUTO_PHY to 0x5a.

5. When the network cable is unplugged, the value of AUTO_PHY is 0x5a.

6. After plugging the network cable, the value of AUTO_PHY is 0x1a.

7. The software sets the value of the register AUTO_PHY to 0x5a.

8. The value of AUTO_PHY is 0x1a (the network cable is still plugged)

Question:

1. Why does plugging/unplugging the network cable on the dp83tc811r cause changes in the AUTO_PHY register?

2. Why does the value of the BMSR register change to 0x65 after the network cable is plugged in? The value is interpreted as a link success as described in the documentation, but it does not indicate the current rate.

Thanks.

  • 0
    TI__Mastermind 18425 points

    Hi Annie,

    Thanks for reaching our over E2E. Someone from our team will get back to you early next week.

    -Regards

    Aniruddha

  • 0 in reply to Aniruddha Khadye
    TI__Mastermind 23675 points

    Hi Annie,

    The AUTO_PHY register is a COR register.

    Also, this register is effected by energy detection on the MDI.

    If you read the register the bit is clear and if energy is detected on the MDI (cable) the bit is cleared.

    Register 0x1 (BMSR) indicated link is up. 

    The device does not support 100BASE-TX, 10BASE-T or 1000BASE-T, which is why those bits are not set.

    It supports 100BASE-T1 since this is a single-pair Ethernet PHY. The speed is always fixed to 100Mbps.