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DP83TG720S-Q1: How to implement an interrupt when link down on DP83TG720S-Q1?

Part Number: DP83TG720S-Q1
Other Parts Discussed in Thread: TDA4VH

I need to use the DP83TG720S-Q1 PHY chip to implement an interrupt when link down. In my tests, I found that register[0x12].13(Link status change interrupt status) is set and the INT_N is set low only when link up. I don't find the relevant register for link downconfiguration , does this PHY support this function?

  • Hi Cao,

    Are you saying that INT_N is LOW when link is up and HIGH when link is down?

    You can enable the link status change interrupt through register 0x12[5] and adjust the interrupt pin polarity in register bit 0x11[3]. 

    Best regards,

    Melissa

  • Hi Melissa,

    I wonder whether the act of removing the 1000BASE-T1 cable (link down) can trigger the PHY interrupt on INT_N, currently it seems that only connecting the T1 cable (link up) can trigger the interrupt.

    Regards, Cao

  • Hi Cao,

    Once an interrupt event flag is set, register access is required to clear the interrupt event. So you will need to read register 0x12 to clear the interrupt. 

    The INT_N pin will be able to detect any change in link status as long as the register is cleared.

    Best regards,

    Melissa

  • Hi Melissa,

    Thank you, I just solved my problem. It is a problem from PHY's state machine.

    In the ti-processor-sdk-rtos-j784s4-evm-09_01_00_06 environment of TDA4VH, when disconnecting the 1000BASE-T1 cable, the PHY state will switch from LINKED state to FOUND state. This state will perform a hardware reset, causing register 0x12 [13] bit to be reset. This can explain that I can observe 0x12 [13]=1 and INT_N=0 only when connecting the 1000BASE-T1 cable.

    In addition, I found a phenomenon that a hardware reset will temporarily set the INT_N of DP83TG720S to 0, while DP83TC812S will not.

    Regards, Cao