iMX7 RGMII rise/fall time spec. with different operation voltage.

[justin_hsieh]

Dear Team,

According to iMX7 Spec., the rise/fall time spec should not over 0.75ns.

There was too hard to meet when RGMII operation in 3.3V.

We find a document that " OPEN Alliance RGMII EPL"., the document was attached.

The shows there are operation in 3.3V, and specify maximum rise/fall time spec.is 1ns

Normaly, RGMII operation voltage is 2.5V, so rise/fall time spec. 0.75ns should not be a problem.

When RGMII operation in 3.3V, should we still follow the 0.75ns spec., or we can just make sure rise/fall time small than 1.0ns.

Please advise.

Justin.

[justin_hsieh]

Hi Yuri,

RGMII and GMII are similar which use the same clock - 125MHz.

RGMII often operation in 2.5V, but GMII operation in 3.3V.

RGMII speify Tr/Tf < 0.75ns.

GMII specify Tr/Tf < 1.0ns.

We know the higher voltage needs bigger rise/fall time.

So, Should we follow the 1.0ns spec.with 3.3V operation? 

Please see the attachement, there is NXP LS1088A datasheet.

There shows 1.8V/2.5V, two different rise/fall time spec which are 0.75ns and 0.54ns.

I think there will be an other rise/fall time for 3.3V operation, right?

Please advise,

Tks.

[Yuri · Accepted solution]

@justin_hsieh 
Hello,

  i.MX7 has not been tested / specified for 3.3V ENET operations,
nevertheless following the 1.0ns spec.with 3.3V operation looks reasonable.

Regards,
Yuri.

[Yuri]

@justin_hsieh 

Hello,

    mainly it is important to consider timing budget and guarantee proper delays and setup / hold 
timings for reliable operations.

https://www.ti.com/lit/an/snla243/snla243.pdf

Regards,
Yuri.