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XIO2001 drive capability

Frank Porfido
Prodigy 60 points

Other Parts Discussed in Thread: XIO2001

I have a design using the XIO2001 to drive a compactPCI backplane. The PCI side of the chip is also conneceted to an Altera FPGA with the pins cofigured as unused with weak pullups.   All works fine at 33MHz for up to 4 cPCI cards in the backplane.  Once I add a 5th card (crate is not full), I can no longer enumerate any of the cards.  If I slow the clock down to 25MHz with sel pin the system works again.  This sounds like a loading issue.  Does anyone have experiance with how many loads the chip can drive at 33MHz?  Is there any way to make it drive harder?

 

Thanks

Frank

  • 0
    Prodigy 60 points

    Sorry one typo correction.  "crate is NOW full"

     

    Frank

  • 0 in reply to Frank Porfido
    TI__Guru* 76130 points

    Hello,

    Can you share your schematic?

    Make sure you are following the interrupt mapping described on Table 2 of the Implementation Guide.

    Regards.

  • 0 in reply to Elias Villegas M.
    Prodigy 60 points

    Elias,

      Thanks for the reply.  I could possibly share my schematic but it could not be through the forum and NDAs would need to be in place.  My connection is fairly simple.  My card is the slot 0 controller so the XIO2001 INTA connects to INTA on the backplane connector, INTB to INTB, INTC to INTC and INTD to INTD.  The routing on table 2 of the implentation quide is done in the cPCI backplane itself.  Also when we slow the PCI clock down to 25MHz everything works with our card in the system slot and 5 addtionaly cards in backplane.  Interrupts are also working in this situation, so I don't think this is an interrupt routing issue.  Please tell me if you disagree. 

    The fact that our system card plus 4 addtional cards works at 33MHz, But our card plus 5 addtional cards doesn not work at 33MHz.  When we slow the PCI clock down to 25MHz both setups work.  This leads me to believe this is a loading issue.  Do you concurr?  Do you have any experiance with how many loads the chip has been know to succesfully drive without an issue?  

    Thanks

    Frank

  • 0 in reply to Frank Porfido
    TI__Guru* 76130 points

    Hello Frank,

    You are correct, this is likely a loading issue. Is it OK for you to slow the clock down to 25MHz? If not, you may need to place a buffer to extend the loading capabilities. 

    Regards.