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DP83867E: IO_IMPEDANCE_CTRL

na na78
Guru 16770 points

Part Number: DP83867E

Hi

I want to confirm about IO_IMPEDANCE_CTRL register.

1.

According to datasheet, the lowest being 11111 and highest being 00000.

So that means 11111 represents 35ohm and 00000 represents 70ohm, is it correct?

2.

If IO_IMPEDANCE_CTRL register is read without any change, that value represents trimmed value for 50ohm but the value is varied by each device.

Is it correct?

3.

Could IO_IMPEDANCE_CTRL register be used regardless of MAC interface (RGMII/SGMII)?

BestRegards

  • 0
    TI__Mastermind 26320 points
    Hi,

    1. Yes, your understanding is correct.

    2. Trimmed values gets over-riden by register configured value.

    3. What's the application you are looking for ? Impedance control is common across MAC interface.

    Regards,
    Geet
  • 0 in reply to Geet Modi
    Guru 16770 points
    Hi Geet

    Thank you for your reply.

    >2. Trimmed values gets over-riden by register configured value.
    Yes, I understand it.

    However, what I want to confirm is the reading value from register in default may not be the same by devices.
    Normally, I believe user doesn't need to change the register value by configured value if the trace impedance is 50ohm.
    If the trace impedance is not 50ohm, the user can change register by configured value. (1bit is corresponding ~1ohm, I think)

    Is my understanding correct?


    >3. What's the application you are looking for ? Impedance control is common across MAC interface.
    Application is IP camera. MAC interface would be RGMII.

    BestRegards
  • 0 in reply to na na78
    TI__Mastermind 26320 points
    Hi ,

    Yes, device default shall be at 50 Ohms and if trace impedance is controlled at 50ohm, register configuration shall not be needed. However if impedance matching is not perfect,, this register configuration can be used to calibrate.



    Regards,
    Geet
  • 0 in reply to Geet Modi
    Guru 16770 points
    Hi Geet

    Thank you. I understood.

    BestRegards