driver output impedance of the RGMII_1 and RGMII_2 signals from the AM335x

Vageesh KM

Hi,

Please let us know the driver output impedance of the RGMII_1 and RGMII_2 signals from the AM335x to provide the series termination on these pins.

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi Vageesh,

The information about required series termination is usually provided in the PHY datasheet or design guidelines.

0 Vageesh KM over 10 years ago in reply to Biser Gatchev-XID

Expert 1075 points

Thanks Biser, will check on PHY datasheet.

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

Hi Biser,

Normally PHY chip manufacturers provide only the source termination resistor values (for the RGMII_RX pins from PHY chip) as per the driver ability of the PHY chip. They wont usually give the termination resistors values in the transmitter side (AM335x/Processor side).

So kindly let us know the driver output impedance of the AM335x RGMII Tx pin pad's.

Thanks & Regards

Sharvy Mayan

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

Hi Biser,

Normally PHY chip manufacturers provide only the source termination resistor values (for the RGMII_RX pins from PHY chip) as per the driver ability of the PHY chip. They wont usually give the termination resistors values in the transmitter side (AM335x/Processor side).

So kindly let us know the driver output impedance of the AM335x RGMII Tx pin pad's.

Thanks & Regards

Sharvy Mayan

0 Biser Gatchev-XID over 10 years ago in reply to Sharvy Mayan

TI__Guru**** 393215 points

Feedback from the factory team: This information is contained as part of the IBIS model.

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

I have already gone through the IBIS model of AM335x.I am not able to get the exact drive impedance of the RGMII pin because of these pins are muxed with multiple signals.
So could you please get back a feedback from the factory team regarding the drive impedance on RGMII pins?

Thanks & Regards

Sharvy Mayan

0 Biser Gatchev-XID over 10 years ago in reply to Sharvy Mayan

TI__Guru**** 393215 points

These are 50 Ohm single-ended impedance lines.

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

The driver output impedance 50 Ohm means we don't need any additional series termination on the RGMII Tx lines.Correct me if I am wrong.

Thanks & Regards

Sharvy Mayan

0 Biser Gatchev-XID over 10 years ago in reply to Sharvy Mayan

TI__Guru**** 393215 points

I cannot say without knowing what PHY you plan to use.

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

Regardless of the phy chip,there should be some definite source resistance ( on the die ) on the pins of RGMII Transmit side of your AM335x device.Our PHY chip recommended to use 22E series resistor on the Rx lines,which is driving from the PHY end (PHY chips source resistance is around 33E).

So,please provide us the source impedance/drive impedance value on the RGMII Tx pad's.

Thanks & Regards

Sharvy Mayan

0 Biser Gatchev-XID over 10 years ago in reply to Sharvy Mayan

TI__Guru**** 393215 points

What information is available has already been posted on this thread. You can also use AM335X design files as a reference: http://processors.wiki.ti.com/index.php/AM335xBoards

0 Sharvy Mayan over 10 years ago in reply to Sharvy Mayan

Intellectual 680 points

Hi Biser,

To get more clarity on the query,please find the attached image for your reference.

Thanks & Regards

Sharvy Mayan

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

Hi Biser,

To get more clarity on my query.Please refer the attached image.

Thanks & Regards

Sharvy Mayan

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

Hi Biser,

Please find the attached image for more clarity on the query.

Thanks & Regards

Sharvy Mayan

0 Biser Gatchev-XID over 10 years ago in reply to Sharvy Mayan

TI__Guru**** 393215 points

I think I already explained that the I/O buffer drives 50 Ohm. No serial resistors are necessary for the TX lines if the PCB traces are routed as 50 Ohm single-ended impedance lines. See also http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist#Ethernet

Please do not post the same question multiple times.

0 Sharvy Mayan over 10 years ago in reply to Biser Gatchev-XID

Intellectual 680 points

Hi Biser,

Thanks for your valuable feedback.

Thanks & Regards
Sharvy Mayan

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driver output impedance of the RGMII_1 and RGMII_2 signals from the AM335x