DP83849IF: Media converter : Strap/Register settings

Hello Yash,

Could you please give me more details on your application and why a dual-port PHY is being used?

What mode are you configuring each of these PHYs to? Are you using pin-strapping and just reading back the register values or have you configured the registers as well?

Thanks,

Vibhu

Hi,

I need a media converter chip(Copper to optical). That's why I use dual port PHY.

PORTA is connected to RJ45 and PORTB to optical transceiver.

DP83849if is configured as a media converter mode with EXTENDER_EN pin enabled. I am using pin strapping and also I have configured 2 registers(PHYCR-disable auto MDIX and EDCR-disable Energy detect mode). I am reading registers values to confirm the settings.

Please let me know if you need more information.

Regards,

Yash

Hello Yash,

I recommend double checking your strap settings with the datasheet and refer to section 3.4 of https://www.ti.com/lit/an/snla086b/snla086b.pdf to see if you are configuring the device correctly.

Additionally for debugging purposes try enabling auto-neg and auto-MDIX and see if this helps isolate the issue.

Thanks,

Vibhu

Hi,

I checked the strap settings. All strap settings are configured correctly for media converter mode.

Could you please tell me in detail how to use auto-neg and auto-mdix modes for debugging purpose?

Thank you.

Hello Yash,

Thanks for confirming that the straps are correct. Sorry for my previous suggestion about auto-neg and auto-MDIX, it looks like you already have an established link.

On further looking at your registers I noticed that the RBR register is configured to 0x04C1. Please try configuring RBR[12:9] to 1110 as suggested in Table 6-7. of the datasheet. This configures the PHY to media converter mode.In your setup RBR[12:9] is configured to 0010.

Thanks,

Vibhu

Hi Vibhu,

Thanks for your suggestion. As you mentioned, I tried to set the RBR[12:9]  for both ports A & B to 1110. I have read the RBR register value 0x1CC1 .

But the communication does not work..

I tried below setup as described in section 3.4.1 without firmware (no read & no write) to monitor the data on RXD lines for both PORTA and PORTB.

I have noticed that the PORTA - RXD0_A to RXD3_A lines are always 0. These lines show no  pulses when I connect the RJ45 to PC. This means that the PORTB transmit pins are not transmitting.

Can you please tell me why this is happening. Did I miss any other setting?

Another question: Should I use Ethernet crossover cable to connect to computer if I don't use Autoneg and auto mdix feature of dp83849if?

Thank you.

Hello Yash,

Yes, please use Ethernet crossover cable when auto-neg and auto-MDIX are disabled. Please double check to make sure that auto-MDIX is disabled when using the crossover cable.

If this doesn't work DNP the pull-up resistor on RXD2_B/EXTENDER_EN in your schematic.

Thanks,

Vibhu

Hello Vibhu,

Thank you for your answer regarding crossover cable.

If I DNP the pullup on RXD2_B/EXTENDER_EN, how does the PHY configure as media converter mode and How can I check if PORTB is transmitting or not?

Regards,

Yash

Hello Yash,

You can ignore that suggestion about DNP the pull-up. You can either have the pull-up or register configure that bit.

Did the crossover cable help?

Thanks,

Vibhu

Hello Yash,

Is there still an issue here, that you need help with?

Thanks,

Vibhu

Hello Vibhu,

The issue is still there, but I am able to read data from RXD0_A..RXD3_A lines to verify the received data from RJ45.

Could you please answer to my previous question:

When RJ45 is not connected, I could see the default pattern of 62.5MHz signal generated by Dp83849if on the FX transmit differential signals. Is that correct or something wrong ? 

Is this a default pattern generated by fiber port PORTB?

Regards,

Yash

Hello Vibhu,

I still have an issue with the communication. But I am able to read the data from RXD0_A...RXD3_A to verify the data comes from the copper port(computer side).

Could you please answer to my previous question:

When the RJ45 is not connected to computer, I could see the default pattern of 62.5MHz signal generated by Dp83849if on the FX transmit differential signals. Is that correct or something wrong ?

Is this a default pattern generated by FX-port in idle condition?

Regards,

Yash

Hello Yash,

The 62.5 MHz frequency if correct. 100BASE-FX uses 4B5B encoding to increase speed from 100 MHz to 125 MHz. This 125 MHz is cut in two by the NRZI encoding to 62.5 MHz.

Thanks,

Vibhu