DP83849ID: No increase in TX and RX bytes and no activity from processor to PHY chip

Ranjith Kumar

Part Number: DP83849ID

Hi,

We are using DP83849ID Ethernet phy chip in or project. The phy chip is connected to the processor via RMII and the processor we are using is i.MX 6ULL. As told in the previous E2E thread we are using DP83848 driver for this Ethernet phy chip. Our problem is that when we are making static IP connection between our board and laptop, it is showing as connection established in the laptop and in the console it is showing as "Link is Up - 100Mbps/Full - flow control rx/tx". But when we are trying to ping the board from the laptop or vice versa it is showing as "Destination Host unreachable". We checked the cable it is working fine and the procedure for creating static connection is also correct. When we probed the TX line from processor to the phy chip while the ping is initiated from the board, it shows no activity in the line. Also there is no increase in RX and TX bytes when we give ifconfig in the board's console.

over 4 years ago

0 Nikhil Menon over 4 years ago

TI__Genius 11725 points

Hi Ranjith,

The TX lines are inputs to the PHY. If there is no activity on the line after link-up, there may be an issue with the MAC. How is the MAC checking for link before sending data?

Thank you,

Nikhil

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

After removing the extended mode strap in phy chip we are able to ping to the laptop.

Thanks,

Ranjith

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

When we probbed the CLK2MAC pin of Dp83849id the 50MHz clk amplitude is around of 1v. This pin is directly connected to the Processor referance clock input. Can u tell me what might be the cause for this drop in voltage. For termination we have connected 50E resitors from CLK2MAC to ground

0 Nikhil Menon over 4 years ago in reply to Ranjith Kumar

TI__Genius 11725 points

Hi Ranjith,

When making the measurement, are you isolating the CLK2MAC pin from the 50E and processor to avoid additional loading?

Thank you,

Nikhil

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

When we removed that 50E termination resistor the issue has been resolved but the clock pulse amplitude is at 4V instead of 3.3V.

Thanks,

Ranjith

0 Nikhil Menon over 4 years ago in reply to Ranjith Kumar

TI__Genius 11725 points

Hi Ranjith,

During the measurement is the MAC still connected? What is the state of the pin?

Thank you,

Nikhil

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

Yes during the measurement the MAC was still connected and when we probed the MACtoPHY CLK pin the frequency was 50MHz with peak-peak voltage of -1V to 4.2V. This voltage needed to be 0 to 3.3V, isn't it?

Thanks,

Ranjith

0 Nikhil Menon over 4 years ago in reply to Ranjith Kumar

TI__Genius 11725 points

Hi Ranjith,

This may be due to an impedance mismatch.Please isolate the pin from the MAC and measure. Please let me know if you are still seeing issues.

Thank you,

Nikhil

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

It is difficult to isolate the pin from MAC, but anyway we will try isolating it. In the mean time please tell us the method to overcome this impedance mismatch.

Thanks,

Ranjith

0 Nikhil Menon over 4 years ago in reply to Ranjith Kumar

TI__Genius 11725 points

Hi Ranjith,

It's difficult to overcome the impedance mismatch without knowing the impedance of the processor, but it sounds like with 50 ohm terminations, your signal level was too low, and removing the 50 ohm resistors left you with too large of a peak-to-peak signal. You may try using a 33 ohm close to PHY, or 17 ohm resistor to see which gives you the best performance.

Thank you,

Nikhil

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

Thanks for the information. We will try what you have told and let you know the observations.

Thanks,

Ranjith

0 Nikhil Menon over 4 years ago in reply to Ranjith Kumar

TI__Genius 11725 points

Hi Ranjith,

Are you still seeing any issues?

Thank you,

Nikhil

0 Ranjith Kumar over 4 years ago in reply to Nikhil Menon

Intellectual 310 points

Hi Nikhil,

For now had unmounted the termination resistor and it is working fine now.

Thanks,

Ranjith

0 Nikhil Menon over 4 years ago in reply to Ranjith Kumar

TI__Genius 11725 points

Hi Ranjith,

Sounds good, I will be closing this thread. If you have any other issues, please open a new thread.

Thank you,

Nikhil

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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DP83849ID: No increase in TX and RX bytes and no activity from processor to PHY chip