Ethernet PHY register access problem with T2080 (EMI2)

[ammasikaniv]

Hi everyone, i am using T2080 processor. As per T2080 datasheet recommendation (attached image for the reference), i am connecting MDIO & MDC pins fo T2080 EMI2 controller to 1.2V with recommended Pull up resistor values. But i am connecting 1.8V VDDO level ethernet transceiver to my T2080 EMI2 controller. With this design, i am not able access the phy register of my ethernet transceiver. I am suspecting that the voltage level of T2080 EMI2 (1.2V) is not compatible with my ethernet transceiver which is having VDDO level of 1.8V. Kindly clarify that Is it possible to connect 1.8V (with require Pull up  value) to T2080 EMI2 controller? Please suggest on this issue... Thanks in advance.

[alexander_yakov]

If the interface is powered from 1.2V, it generates logic "1" at 1.2V, this may be not acceptable for your PHY, please look PHY datasheet for minimum voltage requirement for logic "1" input.

And viceversa, if the input gate is powered from 1.2V, input voltage applied to this input gate should be not higher than 1.2V plus some specified overvoltage value, in case of EMI2 it is (1.2+0.3) = 1.5V (see Table 2 in device datasheet). If your PHY device is powered from 1.8V, its output signals may be higher than these 1.5V, this may stress and finally damage the T2080 device.

For 1.8V PHY device connection we recommend using EMI1 interface, this interface is powered from LVDD, which may be either 2.5V or 1.8V depending on application.

Have a great day,
Alexander

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[ammasikaniv]

Hi Alexander,

Thanks for your response. I accepted your points. In my actual

design i am using two number of (same kind 1.8V VDDO device) PHY for EMI1

(PHY1) & EMI2 (PHY2). Right now, I have shared EMI1 MDIO/MDC bus to my PHY1

& PHY2. Still,the PHY1 is working and PHY2 is not working. Like in T2080RDB

EVM, we have shared EMI1 bus to two number of realtek transceiver. But the

difference is in EVM EMI1 is 2.5V power and i am giving 1.8V to EMI1. With

this change also, the PHY2 is not accessable. Please give some suggestions

to rectify this issue.

--

Regards,

Ammasi Kani V

On Thu, May 19, 2016 at 10:55 AM, Ammasi Kani V <

[alexander_yakov]

This requires further debugging. Please open a Case to technical support and attach your PHY connection schematic, scope shots (if any) and etc

How I could create a Service Request?

[ammasikaniv]

Hi Alexander,

Thanks for your response. I accepted your points. In my actual

design i am using two number of (same kind 1.8V VDDO device) PHY for EMI1

(PHY1) & EMI2 (PHY2). Right now, I have shared EMI1 MDIO/MDC bus to my PHY1

& PHY2. Still,the PHY1 is working and PHY2 is not working. Like in T2080RDB

EVM, we have shared EMI1 bus to two number of realtek transceiver. But the

difference is in EVM EMI1 is 2.5V power and i am giving 1.8V to EMI1. With

this change also, the PHY2 is not accessable. Please give some suggestions

to rectify this issue.

--

Regards,

Ammasi Kani V

On Wed, May 18, 2016 at 8:31 PM, alexander.yakovlev <