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TMS320C6678: SGMII, AC Electrical characteristics.

erez cohen
Intellectual 595 points
Part Number: TMS320C6678

Hi,

On my design i have the Marvell 88E6185 port 0 connected to the DSP SGMII I/F.

The switch have optional selection of voltage (1.2V or 1.5V) for its SGMII transmitter.

Could you please advise the electrical characteristics of the SGMII I/F? does it comply SGMII Specification (ENG-46158), Version 1.8?

I am trying to understand if i should connect the switch Transmitter voltage to 1.2V or 1.5V.

Thanks,

Erez.

  • 0
    TI__Mastermind 46460 points

    Erez,

    Per the Hardware Design Guide (SPRABI2D), the EMAC interface is compliant with the SGMII Specification (ENG-46158), Version 1.8 which specifies the signal levels.  I am not familiar with a TX level option.  I assume your connection is short-reach.  Therefore, the 1.2V TX amplitude should be the right choice.  Long or lossy connections would need the larger TX level.

    Tom

  • 0 in reply to Tom Johnson 16214
    Intellectual 595 points

    Tom,

    According the TMS320 DS, VDDR3 should be powered by 1.5V. is that mandatory? can it be powered from 1.2V? in case it must be powered by 1.5V how can i set the transmitter to 1.2V signal levels?

    What is defined as Long/Lossy connection what is defined as short/long reach?

    Erez.

  • 0 in reply to erez cohen
    TI__Mastermind 46460 points

    Erez,

    Short reach and long reach are specs for higher speed SERDES.  SGMII is hardly a challenge at 1.25GBd.  The terms are defined by attenuation.  Normally, short reach is a few inches with losses less than 6-10dB at the Nyquist frequency.  Long reach can be over 20 inches with losses over 15dB.  The exact definition changes with interface type and data rate.  Long reach SERDES links need significant TX shaping with lots of pre-emphasis coupled with equalization in the receiver.  The SERDES interface for SGMII in the C6678 supports these features but they are not needed for SGMII unless the links are very long.

    The output swing is fully programmable.  Please see Table 21 in Section 9.3 in the SerDes Implementation Guide for KeyStone I Devices Application Report (SPRABC1).

    Tom