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SN65LVPE501: PCIe repeater chip Rx Detect function

Mark Philip Felipe
Genius 11180 points

Part Number: SN65LVPE501

Hi Team, just for quick clarification about PCIe repeater chip Rx Detect function.


Does the part-turn off (Set to HiZ) it's receiver terminations if it does not detect a receiver on a transmitter?

Thank you very much.

-Mark

  • 0
    TI__Guru* 93570 points

    Hi Mark,

    PCIe specifies high impedance as greater than about 20K-Ohm. When terminated it is specified as 60-ohm +/-15%. So there is a big jump.

    Regards,, Nasser 

  • 0
    Prodigy 20 points

    The response from Nasser does not answer the question.  It gives two impedances presumably for two situations but does not say when the part uses a those impedances.  The data sheet says the if en_rxd is high when rst goes high and is high the part will perform  the rxdetect function on both of its transmitters until it detects a receiver on both transmitters.  It never really says if the rxdetect function has an effect of the receiver impedance.  The data sheet seems to indicate that  only rx_en has an affect on the receiver impedance impedance.  It would be most beneficial if the presence of a receiver would switch the associated transmitters impedance fro High-Z to proper termination.

  • 0 in reply to Carl Hayssen
    TI__Guru* 93570 points

    Hi Mark and Carl,

    Hope i can answer the question clearly. On power up - when enabled through RX Detect pin - device sends out out RX detect pulses on its transmitter toward the end point.

    a). If it detects a 20K ohm or higher on its transmitter - end point RX termination - it assumes there is not termination on its output. In this case, device RX termination - seen typically by the CPU - is also high impedance(>20K ohm).

    b). On the other hand if it detects 60-ohm +/-15% on its transmitter, then it assumes there is a valid termination. In this case, device turns on its own RX 50-ohm termination. This signals the CPU to start PCIe protocol negotiations.

    Regards,, Nasser

  • 0
    Prodigy 20 points

    Thank you! This latest reply does answer the question and  even gives the hoped for answer.  I am guessing that the device will not detect if the far end receiver termination goes to >20k.  It would be difficult to determine teh loss of termination once the system is passing traffic.