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DP83822I: RMII Master and RMII Slave Register Configuration

Swapna yendrapalli
Intellectual 625 points
Part Number: DP83822I

Hi,

We are using DRA821cpsw2g(port1) and cpsw5g(Port1 and Port4) ethernet switches connected to DP83822I IC's.

  • cpsw2g is connected to DP83822I using 25MHz reference clock (RMII Master Mode)
  • cpsw5g is connected to DP83822I using 50MHz reference clock (RMII Slave Mode)

Attaching the schematics for our setup.

/resized-image/__size/640x480/__key/communityserver-discussions-components-files/138/pastedimage1646059449444v1.png

/resized-image/__size/640x480/__key/communityserver-discussions-components-files/138/pastedimage1646059785505v3.png

Could you please let us know the needed register configurations for operating DP83822I IC in RMII master and RMII slave mode?

Thanks,

Swapna

  • 0
    TI__Mastermind 26712 points

    Hi Swapna, 

    The DP83822 mode is configured through bootstrapping.  Refer to section 8.5.1 of the datasheet for more information on this. 

    To put the device in RMII mode, pin 26 should have mode 4 strapping. For RMII slave mode, pin 26 should have mode 3 strapping. This is shown in table 8-10 of the datasheet. Your schematic images are too low resolution for me to check this. 

    You can check if the device is set in RMII mode by reading bit 5 of register 0x0017. Can you read this register back and let me know the results?

    Thanks,

    David

  • 0 in reply to David Creger
    Intellectual 625 points

    Thanks David!

    pin26 has a 3.3V pull up with resistor -2K21.

    Attaching the RMII master and Slave Mode Schematics.

    Please let us the SMI settings to configure the PHY in RMII master and RMII Slave mode.

    We don't have the PCBA's in our hands and will report back.

  • +1 in reply to Swapna yendrapalli
    TI__Mastermind 26712 points

    Hi Swapna, 

    Since all the PHYs in your schematic have pin 26 in mode 4 bootstrapping, they will boot up in RMII master mode. We recommend changing the slave mode PHY to bootstrapping mode 3 instead. 

    If you cannot change the schematic, you can enable RMII mode and select the 25Mhz clock through register 0x0017 (Table 8-36 in the datasheet). After you change these settings, we recommend performing a digital restart by setting register 0x001f to 0x4000.

    Also, why are 2.21kohm resistors being used for the strapping? We recommend 2.49kohm for mode 4 in the datasheet.

    Thanks,

    David 

  • 0 in reply to David Creger
    Intellectual 625 points

    Thanks David! I will check resistor deviation with our hardware team. 

  • 0 in reply to Swapna yendrapalli
    TI__Mastermind 26712 points

    Thank you. Let me know if you have any additional questions. 

    -David