RMII connections - SX and LAN8720

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RMII connections - SX and LAN8720

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Richard1z
Contributor II

I want to use a LAN8720 (RMII) with the iMX6SX.

The IMX6SXHDG does not cover the Ethernet Interface at all.

The SX Reference Manual covers it very badly.

If anyone has got the combination of LAN8720 + SX working correctly, I be obliged if they could review my schematics below or share theirs.

(My biggest cause for concern is the generation of the REF_CLK  - as there seems to continual confusion about this.)

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Richard1z
Contributor II

Hi Weidong.

thank you very much for this helpful information !

R

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weidong_sun
NXP TechSupport
NXP TechSupport

Hello Richard,

See following , please!

(1) ENET1_REF_CLK_25MHz( PAD: NET1_RX_CLK or GPIO1_IO03)

---NET1_RX_CLK or GPIO1_IO03 pin can output 25MHz clock for LAN8720A, not PAD ENET1_TX_CLK, see page 1028 of reference manual.

---About Reference Clock input for CPU

Pad ENET1_TX_CLK can be used to be reference clock input (ENET1_REF_CLK1 signal), but above 25MHz clock can be routed to the pin by internal channel of i.MX6SX, so you don't need to connect external clcok to Pad ENET1_TX_CLK.

(2)Connect 15p capacitor between differential lines

One 15pF capacitor between TXP and TXN

One 15pF capacitor between RXP and RXN

   No other issues were found!

Best regards,

Weidong

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Richard1z
Contributor II

Hi Weidong.

thank you very much for this helpful information !

R

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