DP83867CR: MDIO signal abnormal

Kailyn Chen

Genius 9560 points

Part Number: DP83867CR

Dear，

One customer used DP83867 for his application and found that the MDIO signal is abnormal.

When RESET=0, the MDIO is normal,

but after finishing RESET(RESET=1), MDIO is pull low.

If serial one 100ohm resistor between MAC and PHY, MAC level is normal but PHY is pulled low.

The schematic is attached.

DP83867 PHY (1).pdf

Finally, by referred this post:https://e2e.ti.com/support/interface-group/interface/f/interface-forum/717497/dp83867is-mdio-signal-of-dp83867is

leave the GPIO float, the MDIO signal changed normal. Why? Why the GPIO affect the MDIO signal? Could you please help to analyze how the GPIO affect the MDIO which caused PHY behavior abnormal?

Best regards

Kailyn

over 1 year ago

0 Alvaro (Al-vuh-roe) Reyes over 1 year ago

TI__Mastermind 19621 points

Hi Kailyn,

Thank you for providing the scope shots, but is there a way we can annotate them? I'm not exactly sure as to which signal is what.

I took a look at your schematic and see that MDC has a 10 kΩ pull up resistor to VDDIO. Please remove this. MDIO requires a 2.2 kΩ PU but MDC does not. I hope that this solves your issue.

Regards,

Alvaro

0 Kailyn Chen over 1 year ago in reply to Alvaro (Al-vuh-roe) Reyes

TI__Genius 9560 points

Hi Alvaro，

Thank you very much for your reply.

Alvaro (Al-vuh-roe) Reyes said:
but is there a way we can annotate them? I

I am so sorry that I missed the information of the test channel:

CH1：MDC CH3：MDIO_MAC CH2：MDIO_PHY

Alvaro (Al-vuh-roe) Reyes said:
Please remove this. MDIO requires a 2.2 kΩ PU but MDC does not

The datasheet describes that MDIO should require 2.2Kohm pull up.

Best regards

Kailyn

0 Alvaro (Al-vuh-roe) Reyes over 1 year ago in reply to Kailyn Chen

TI__Mastermind 19621 points

Hi Kailyn,

Kailyn Chen said:
The datasheet describes that MDIO should require 2.2Kohm pull up.

Yes, MDIO requires a 2.2 kΩ PU but MDC does not require the 10 kΩ PU. Please remove the 10 kΩ PU from MDC.

Regards,

Alvaro

0 Kailyn Chen over 1 year ago in reply to Alvaro (Al-vuh-roe) Reyes

TI__Genius 9560 points

Hi Alvaro，

Sorry to interrupt you again.

The customer has removed the 10 kΩ PU from MDC, but it couldn't resolve the problem.

Do you have any other opinion?

Best regards

kailyn

0 Alvaro (Al-vuh-roe) Reyes over 1 year ago in reply to Kailyn Chen

TI__Mastermind 19621 points

Hi Kailyn,

I don't believe I've asked this before, but are you able to read/write registers? I would also like to check the MAC's voltage level. Is it also operating at 1.8 V, like our PHY is?

Regards,

Alvaro

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DP83867CR: MDIO signal abnormal