DP83848I: Questions about DP83848I...

Peter Tseng

Part Number: DP83848I

Hi Sir,

I have questions about DP83848I, please help.

1. customer use DP83848I MII mode and work well.

However, after changing the old modem with a new one and they found the DP83848I can't work, all LEDs are off after the cable is plugged but the MCU still working well in their system.

After software reset DP83848I from MCU, the PHY work finally.

May I have your comments what kind of problem will cause this issue?

2. customer wants to change from MII to RMII, please help to check if there is any problem with their schematics.

Is there any in serial resistor necessary for RMII trace? If yes, where is the suggested place? close to PHY or close to MCU or...?

22001a_220210-001.pdf

Thanks.

over 3 years ago

0 Gokul Koraganji over 3 years ago

TI__Mastermind 19250 points

Hi Peter,

Thank you for the query. Please let me take a detailed look at the schematic and get back to you by Wednesday 16th Feb.

--
Regards,
Gokul.

0 Peter Tseng over 3 years ago in reply to Gokul Koraganji

Mastermind 6170 points

Dear Sir,

Any update?

Thanks.

0 Gokul Koraganji over 3 years ago in reply to Peter Tseng

TI__Mastermind 19250 points

Hi Peter,

Apologies for the delay.

For the RMII mode usage, I strongly recommend going through the following app note https://www.ti.com/lit/an/snla076a/snla076a.pdf
Please find attached, the schematic with annotated comments.
22001a_220210-001_feedback.pdf

Series resistor of 50 ohms is recommended on RX_D, RX_CLK lines. The resistor should be as close to the PHY as possible.

Please let me know if you need more details.

--
Regards,
Gokul.

0 Peter Tseng over 3 years ago in reply to Gokul Koraganji

Mastermind 6170 points

Hi Sir,

Thanks for the reply!

May I have your comments about question #1?

Thanks.

0 Gokul Koraganji over 3 years ago in reply to Peter Tseng

TI__Mastermind 19250 points

Hi Peter,

Can you please let me know the following?

Are the old and new modem from the same vendor?
What is the register setting used for software reset which made the link re-established?
What is the speed chosen 10M/100M? Is auto-negotiation enabled?

0 Gokul Koraganji over 3 years ago in reply to Gokul Koraganji

TI__Mastermind 19250 points

Hi Peter,

Were you able to resolve the issue? Else, can you please respond to the questions above?

--
Regards,
Gokul.

0 Peter Tseng over 3 years ago in reply to Gokul Koraganji

Mastermind 6170 points

Hi Sir,

Here is the information update for you.

Thanks.

Are the old and new modem from the same vendor?

-> They are different vendor modem. actually, the issue occurred while changing the modem in an in-complete network loop!

After the network loop is completed, the issue was fixed.

What is the register setting used for software reset which made the link re-established?

-> customer cannot duplicate the issue and just monitor the host side. If there is no valid payloads over 18mins, they will reboot the device by PHY reset pin (pin29)

What is the speed chosen 10M/100M? Is auto-negotiation enabled...

-> customer use 100M, auto-negotiation was enabled.

0 Peter Tseng over 3 years ago in reply to Peter Tseng

Mastermind 6170 points

Hi Sir,

Some additional information share with you!

In customer network loop, there are total 20 nodes(modems) on it. Once the modem needs to be replaced and after changed with new modem then re-power on(new modem), all others modems on same loop will shutdown.

Maybe it is not the issue caused by the PHY, but may I have your comments why the PHY will shutdown?(for example, PHY will got some signal or payload data in such situation)?

Thanks.

0 Gokul Koraganji over 3 years ago in reply to Peter Tseng

TI__Mastermind 19250 points

Hi Peter,

The ethernet PHY DP83882 will not shut down even when any modem is replaced. The PHY will still try to link-up with the new modem.

It is easy to monitor whether it is a PHY issue. You can monitor reg<0x0001>[2] which is link status. If the link status is 1 after reading it twice, then the issue is not with the PHY. Instead, you can monitor LED_LINK (pin 28).

Please let me know if you need more details.

--
Regards,
Gokul.

0 Peter Tseng over 3 years ago in reply to Gokul Koraganji

Mastermind 6170 points

Dear Sir,

Thanks for your information!

However, per customer feedback, all LEDs will be off while the issue occurred...

0 Gokul Koraganji over 3 years ago in reply to Peter Tseng

TI__Mastermind 19250 points

Hi Peter,

We might have to read some of the device registers during the link down condition to check what is the issue.
Since the issue can't be recreated, the issue might be some loose connection of cable or supplies.

Can you please check if the customer can recreate the issue so that we can look into it further?

--
Regards,
Gokul.

0 Gokul Koraganji over 3 years ago in reply to Gokul Koraganji

TI__Mastermind 19250 points

Hi Peter,

I'm assuming this issue is resolved due to inactivity. Please get back to me for any other queries.

--
Regards,
Gokul.

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DP83848I: Questions about DP83848I...