LS1021A Ethernet interface - RGMII 3.3V support

[senoghte]

Hi

We want to use LS1021, RGMII (TSEC3) and MII(TSEC1) simultaneously. we have two notes that said "1. RGMII is supported at 2.5 V or 1.8 V. RMII/MII are supported at 3.3 V."

and another note that "7. LVDD and L1VDD must always be the same voltage. This also applies to DVDD and D1VDD"

but in Reference manual and other application notes we do not see any conflict of selecting both RGMII and MII simultaneously.

In other side I want to use devices that can support 2.v and 3.3v RGMII and MII.

what is the solution?

I think to below ways:
1. connect both LVDD and L1VDD to 3.3v and Use other device  MII in 3.3v and RGMII in 2.5v (or 3.3v)

OR

2. use different voltages for L1vdd(3.3v) and LVDD(2.5v) and use RGMII in 2.5v and MII in 3.3v?

another question asked in :

LS1021A Ethernet interface - MII 2.5V/1.8V support 

but the answer is not clear.

Thanks

[ufedor]

1) Electrically it is possible to power RGMII interface by 3.3V (LVDD=L1VDD=3.3V).
Please consider that RGMII interface operation was characterized only for 1.8V and 2.5V – i.e. no timings for 3.3V operation are provided, thus 3.3V operation is not officially supported.

2) You wrote:

> use different voltages for L1vdd(3.3v) and LVDD(2.5v)

The processor will be damaged in this case.

[senoghte]

Hi

Thanks a lot for your previous answer. according to your answer we decided to use eTSEC1 in MII and eTsec3 in RGMII mode but connect both L1VDD and LVDD to 2.5v and manage possible MII problems with timing barriers of course another side of this MII interace is supporting 2.5v.

But we have another problem with some sentences in AN4878 table 31 that "When eTSEC 1 or eTSEC 2 are configured as MII mode some of the MII 1 and MII 2 signals are muxed with eTSEC3 signals. In the RCW configuration eTSEC 3 must be selected as MII" . does it mean that RCW[EC3] can not be set 000 when we use eTSEC1 in MII? MII optional pins not used.

Refer to table 4-14 of LS1021RM we want to set RCW[EC1]=011(MII) and RCW[EC3]=000(RGMII). this doesn't cause any conflict in register settings. May we assume it is possible?