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i.MX6 - Ethernet PHY Interface

Question asked by Durmuş Kurtuluş on Jul 23, 2014
Latest reply on Jul 25, 2014 by igorpadykov

Hello all,

 

We're currently designing a custom board based on SABRE SDP. We chose to use KSZ9021RN as ethernet PHY.

We're having some difficulties about the voltage levels.

In our design:

i.MX6:

NVCC_RGMII = 2.5V and NVCC_ENET = 3.3V as in SABRE SDP.

KSZ9021RN:

AVDDH = 3.3V, DVDDH = 2.5V (similar SABRE SDP's configuration with AR8031).

 

Since the voltage domain of the signals RGMII_MDC, RGMII_MDIO, ENET_REF_CLK, RGMII_INT is NVCC_ENET,

it seems to me that a voltage level translation is needed for these signals. However, in SABRE SDP, a level translator

exists only for ENET_REF_CLK.

 

In datasheets of both AR8031 and KSZ9021RN, it says that an external pull-up resistor is required to 3.3V/2.5V digital VDD

for MDIO and INT. Since RGMII 2.5V is used in SABRE SDP, I believe it should be the latter (2.5V), yet they are tied to 3.3V.

 

What am I missing here? This issue confuses me a lot and I cannot be certain of the connections in our design.

 

Can anyone clarify this issue?

 

Thanks in advance.

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