DP83826E: RMII mode crystal oscillator

Fabio Gou

Part Number: DP83826E

1. DP83826E chip, the customer is using RMII mode. The crystal oscillator should be 25MHz or 50MHz?

Besides, for the RMII slave mode, it means the DP83826 is slave, and the MUC ARM is host. Is it right?

2. If the interface does not want to use a transformer, RX/TX only needs to connect a 33nf capacitor in series? Do it still need to pull up to 3.3V or 5V?

3 months ago

0 Alvaro (Al-vuh-roe) Reyes 3 months ago

TI__Genius 15746 points

Hi Fabio,

There are two flavors of RMII: Master and Slave
1. Master
  1. In Master Mode, the PHY operates off of a 25 MHz input clock.
  2. PHY outputs a 50 MHz ref_clk that can be connected to the MAC
2. Slave
  1. In slave mode, the PHY operates off of a 50 MHz input clock that needs to be shared between the PHY and the MAC
    1. An alternative solution would be for the MAC to provide the 50 MHz clock to the PHY
3. Section 9.3.10 Reduced Media Independent Interface (RMII) in the data sheet has more detailed information, please carefully read this section.
No pullup is needed for the DP83826's connector side circuit. Please follow the diagram you attached for Capacitive DC blocking

Regards,

Alvaro

0 Fabio Gou 3 months ago in reply to Alvaro (Al-vuh-roe) Reyes

TI__Intellectual 2860 points

May I ask if the RMII slave mode crystal oscillator must use an active crystal oscillator? Can a passive crystal oscillator be used?

0 Alvaro (Al-vuh-roe) Reyes 3 months ago in reply to Fabio Gou

TI__Genius 15746 points

Hi Fabio,

Either may be used. Keep in mind that for RMII Slave, that 50 MHz clock needs to be shared between both the PHY and MAC.

Regards,

Alvaro

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DP83826E: RMII mode crystal oscillator