topic Re: LS1021A Ethernet interface - MII 2.5V/1.8V support in Layerscape

LS1021A Ethernet interface - MII 2.5V/1.8V support

fdm — Wed, 03 May 2017 16:05:22 GMT

Hi,

I need to use both RGMII and MII interfaces simultaneously in a new LS1021A based board.

According to the LS1021A datasheet, all Ethernet interfaces should have the same supply voltage LVDD = L1VDD, and this voltage should be 1.8V or 2.5V when RGMII is used, but MII is specified at 3.3V only (unlike e.g. T1040 that has MII specifications at 2.5V and 3.3V).

Can the LS1021A Ethernet controller be used in MII mode with 2.5V and/or 1.8V supply? Is there any examples of such usage?

BR,
Denis

Re: LS1021A Ethernet interface - MII 2.5V/1.8V support

r8070z — Thu, 04 May 2017 05:01:27 GMT

Have a great day,

The LS1021A data sheet says “1 RGMII is supported at 2.5 V or 1.8 V. RMII/MII are supported at 3.3 V” and “7 LVDD and L1VDD must always be the same voltage” on the same page. Hence using MII at 2.5V you definitely violate the LS1021 specifications.

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Re: LS1021A Ethernet interface - MII 2.5V/1.8V support

fdm — Thu, 04 May 2017 07:49:14 GMT

Serguei,

Would you provide some background information on this?

Has the MII interface at 2.5V been tested and confirmed to be non-functional or it just isn't characterized yet?

In the case of e.g. T1040 this 2.5V MII mode had been characterized starting with the rev.1 of DS.

Re: LS1021A Ethernet interface - MII 2.5V/1.8V support

r8070z — Thu, 04 May 2017 12:47:44 GMT

I believe it just isn't characterized yet. I did not see any problem report for MII at 2.5V. By the way QorIQ LS1021A Design Checklist, Rev. 3, 12/2016 (AN4878) has table

while both EC2 and EC3 are connected to the LVDD and RMII on the EC3 should be at 3.3V acoording to the data sheet. I also think that requirement that "LVDD and L1VDD must always be the same voltage" also is related to mix of the L1VDD and LVDD signals on some interfaces. Hence the configuration EC1 RGMII at 2.5 V and MII on the EC3 at 3.3V also is possible at some condition with workarround for the managment interface (2 signals) for the RGMII PHY.

However I am not sure. You may try to create a technical case to the nxp support for confirmation.