DP83867IRPAP RGMII termination

Thomas Kofoed-Hansen

Other Parts Discussed in Thread: DP83867CR

The datasheet has the following statement on the first page.

"Programmable MII/GMII/RGMII Termination Impedance"

Is this to be understood as output impedance?

I haven't been able to find any settings or registers to control this impedance. I'm asking because we have to run our RGMII bus through an analoug switch which puts extra load on the signals. This load together with the "normal" output impedance of a PHY makes it impossible for us to match timing on an fpga. If we could lower the output impedance we could hopefully counteract the extra load.

There are also other interesting things/features of this PHY but this is right now the most important.

Thomas

over 9 years ago

0 Thomas Kofoed-Hansen over 9 years ago

Intellectual 550 points

Just want to check if someone has seen my request and that an answer is on its way.

0 Patrick OFarrell over 9 years ago in reply to Thomas Kofoed-Hansen

TI__Mastermind 31600 points

Thomas,

I apologize for the delay. Our U.S. offices were closed for part of last week.

What is the loading presented by the analog switch? What is the impact of this loading on the timing? Are you seeing skew between the clock and data lines?

Patrick

0 Thomas Kofoed-Hansen over 9 years ago in reply to Patrick OFarrell

Intellectual 550 points

Patrick,

the routing is ideally 50 Ohms, then there is the input capacitance of the receiver. All most all PHYs I have encountered have some kind of internal series termination and drive the signals with an impedance close to the 50 Ohms. With the added switch in the path it causes longer rise and fall times. The skew is minimal, it's the effect on the rise and fall times that impacts the timing.

It's easy to add series termination to a signal path but it's impossible to lower an internal series termination. This is why I asked about the "Programmable MII/GMII/RGMII Termination Impedance" statement in the datasheet.

In the revision history I can even see that this statement has deliberately been added to the datasheet after the first revision.

Thomas

0 Thomas Kofoed-Hansen over 9 years ago in reply to Thomas Kofoed-Hansen

Intellectual 550 points

Patrick,

Not to put any pressure on you, but I need to make a decision very soon, so have you fund out what the mentioned statement is about and what it means?

Thomas

0 Thomas Kofoed-Hansen over 9 years ago in reply to Thomas Kofoed-Hansen

Intellectual 550 points

Is there an Programmable MII/GMII/RGMII Termination Impedance on the DP83867CR as stated on the front page of the datasheet?

0 Rob Rodrigues over 9 years ago in reply to Thomas Kofoed-Hansen

TI__Mastermind 19780 points

Hi Thomas,

Yes there is. The datasheet has been updated with this information. Please check the datasheet posted for the DP83867CR. Find the information in the register table for register address 0x0170.

Best Regards,

0 Thomas Kofoed-Hansen over 9 years ago in reply to Rob Rodrigues

Intellectual 550 points

Thank you Rob.

I don't know how we could miss this, but most importantly your question solved our question perfectly.

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DP83867IRPAP RGMII termination