DP83848I-MAU-EK: Can I replace a circuit based on the LXT905 with the DP83848I-MAU-EK board? And what mode of operation is recommended: MII or SNI?

Hi Said,

Can you please share more details on the system requirements - is SNI required, and is the data rate fixed at 10M?

While SNI has a smaller footprint due to fewer trace connections, it may be more challenging to find an SoC supporting this interface (relative to MII/RMII/...).

I recommend looking at our newer industrial PHYs to see if they might fit the system requirements:

DP83822, DP83825, DP83826

Thank you,

Evan

Hi Evan,

     Thank you for replay, my system need 10M data rate, it's defined as "Universal Transceiver offers 10BASE-T connectivity". As LTX905, the system uses 20MHz Crystal Oscillator and a 10 MHz clock output at TCLK pin "Transmit Clock". TXD "Transmit Data" use NRZ code to transmit data. It use the folowing pins, I show a comparison with DP83848C pins in SNI mode :

     Thank you for your reply. My system requires a 10 M data rate and is defined as 'Universal Transceiver offers 10BASE-T connectivity.' Based on the LXT905, my system uses a 20 MHz crystal oscillator and a 10 MHz clock output at the TCLK pin for 'Transmit Clock.' The TXD (Transmit Data) signal uses NRZ coding to transmit data.

Here's a comparison of the pinouts between the LXT905 and DP83848C in SNI mode:

DP83848C    (SNI mode)                           LTX905

• TX_CLK                                          TCLK
  
• TX_EN                                             TEN
  
• TXD[0]                                             TXD
  
• RX_CLK                                          RCLK
  
• RXD[0]                                            RXD
  
• CRS                                                  CD "Carrier Detect"
  
• COL                                                 COL

Do you need any more information?

Another question please : To choose between SNI or MII mode, do we only need to configure the MII_MODE (RX_DV) and SNI_MODE (TXD_3) pins according to the table? Or do I need to program the evaluation board with specific software?

Thank you

Said

Hi Said,

Thank you for sharing the detailed comparison.

DP83848I-MAU-EK can be configured in SNI mode, if you have an SoC to connect its SNI breakout pins to for evaluation.

One concern I have is the 20MHz crystal oscillator in your current system - DP83848 XI input clock must be 25M +/-  50ppm.

FARAH Said said:

To choose between SNI or MII mode, do we only need to configure the MII_MODE (RX_DV) and SNI_MODE (TXD_3) pins according to the table?

This is correct, RX_DV and TXD_3 are the only straps required to set SNI mode.

Best Regards,

Evan

Hi Evan,

     Thank you for your respense.

     I steel have problem, d'ont work for me but I've noticed that to configure the DP83848I-MAU-EK for SNI mode, we need to set the following pins: 

• RX_DV = High
• TXD_3 = High

And also :

• AN_EN = Low
• AN0 = Low
• AN1 = Low

However, I don't see these pins (AN_EN, AN0, AN1) on my DP83848I-MAU-EK evaluation board. How can I configure these pins to enable SNI mode?

Thank you for your help.

Said

Hi Said,

Setting {AN_EN, AN0, AN1 = low} should not be required for operation in SNI, unless auto-negotiation link speed is resolving to 100M.

Which link partner would DP83848 be connected to on cable-side? If this link partner supports only 10M auto-negotiation, I expect this to work for SNI.

If the link partner does not have compatible auto-negotiation settings, MDC/MDIO pins can be used with external launchpad to program the required mode.

For link partner with auto-negotiation enabled:

• Disable 100M advertisements on both PHYs (write 0x4[8:7] = '00')

For link partner with forced 10M speed (auto-neg disabled):

• Write 0x0[13:12] = '00' to disable auto-neg and force 10M

Thank you,

Evan