DP83848C: Auto negotiation failed with router

anishkumar singh

Part Number: DP83848C

I am having a board which is based on Keil MCB1700, i have attached the schematic.

I have added DHCP client in one of the examples. I tested this code by directly connecting the board to laptop.

Now when connecting to wifi router[Dlink DIR-605L] i am not able to get IP address.

By monitoring LINK leds and reading PHYSTS register, i found that the link is not stable i.e link speed toggles between Full/Half duplex & 10/100 mbps frequently and auto-negotiation never succeeds.

This is not the case when i connect board directly to laptop, the link very stable i.e Full Duplex, 100Mbps

LPC1768 HPLUS EX.pdf

over 8 years ago

0 Ross Pimentel over 8 years ago

TI__Mastermind 23675 points

Hi Anishkumar,

Thank you for the schematic and information above.
I do not see any termination resistors for TD+/- or RD+/- in the schematic.
The DP83848 is a CML and requires 50 ohm termination to VDD.

Can you check if your board has this?

Please refer to Figure 7-2 in the DP83848C datasheet (section 7.2.1.1).

Kind regards,
Ross

0 anishkumar singh over 8 years ago in reply to Ross Pimentel

Expert 1060 points

I checked the board, termination resistor is not placed it has ZERO ohm.

Right now we don't have 50 ohm will 51ohm & 1uf be ok?

Any reason why communication between laptop and board is working with out termination resistor?

0 Ross Pimentel over 8 years ago in reply to anishkumar singh

TI__Mastermind 23675 points

Hi Anishkumar,

For now 51 ohm is better than no termination.
However, we do have a specified termination value in the datasheet to ensure you are within IEEE 802.3 compliance.
The current mode line driver will not work properly without termination to 3.3V.

Kind regards,
Ross

0 anishkumar singh over 8 years ago in reply to Ross Pimentel

Expert 1060 points

Hi Ross,

We are experiencing same issues as mentioned in previous posts, even we added the termination resistor[50ohm] as per application circuit in DP83848C.

0 Rob Rodrigues over 8 years ago in reply to anishkumar singh

TI__Mastermind 19780 points

Hi Anishkumar,

Does your router support auto-negotiation? Some do not. You should check DP83848 register 0x5 to see if the router is transmitting auto-negotiation pulses.

Next steps would be forcing link speed, duplex, and MDI/MDI-X setting from the DP83848 to see if you can establish communication with the router.

Best Regards,

Interface

Interface forum

DP83848C: Auto negotiation failed with router