DP83867IR: RGMII Timing Constraints and Figures from Documentation

Zachary Handzel

Part Number: DP83867IR

Hi there,

I have been looking at the datasheet for this product and am confused as to how the pictures conform to the actual settings. Figure 4 is labeled Transmission but has TskewR, which relates to the receiver, and Figure 5 is labeled Receiving bu has TsetupT and TholdT, which relate to the transmitter. This is all very confusing. Could anyone elaborate on how these figures work?

over 6 years ago

0 Aniruddha Khadye over 6 years ago

TI__Mastermind 18425 points

Hi Zachary,

When data is going out on the cable (Transmission) it will typically originate at the MAC and be sent to PHY over the RGMII TX interface. In this case the MAC is the transmitter and the PHY is the recevier. The TskewT in this case refers to the Skew at MAC and TskewR referes to the PHY. The over all process is still tagged Transmission since the data eventually ends up on the cable.
This naming convention is used in the datasheet in order to match the naming convention in the RGMII standard.

-Regards,
Aniruddha

0 Zachary Handzel over 6 years ago in reply to Aniruddha Khadye

Prodigy 30 points

Thank you and does this also apply for Figure 5 so that the PHY is the transmitter and TsetupR and TholdR are constraints put on the receiver (MAC)?

0 Aniruddha Khadye over 6 years ago in reply to Zachary Handzel

TI__Mastermind 18425 points

Hi Zach,

Yes, the same logic would apply to RGMII receive timing.

-Regards,
Aniruddha

0 Zachary Handzel over 6 years ago in reply to Aniruddha Khadye

Prodigy 30 points

Hi Aniruddha,

Thank you very much! This helps quite a bit but I am curious does that also mean that an assumption is made about the MAC's setup and hold for receiving or is this an actual requirement? I've looked at some data sheets for other phy models and they generally only include constraints for the phy.

-Thank you again,
Zach

0 Aniruddha Khadye over 6 years ago in reply to Zachary Handzel

TI__Mastermind 18425 points

Hi Zach,

Since the MAC would also need to be RGMII compliant, it would also meet the setup and hold time requirements as specified by the RGMII. The only assumption made here (for DP83867) is that the MAC does not add any internal delay of its own. If it does either the delay on the MAC side or the PHY side would need to be disabled.

-Regards,
Aniruddha

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DP83867IR: RGMII Timing Constraints and Figures from Documentation