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Thread: PCI bus

  1. #1
    Constant Bitrate weekendowel's Avatar
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    PCI bus

    Is it possible to wire two PCI cards in parallell? Anyone know how a dual riser card is connected to the PCI bus?

  2. #2
    Raw Wave tj!2k4's Avatar
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    multi-slot riser cards have a connector for each pci slot.

  3. #3
    Constant Bitrate weekendowel's Avatar
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    Yes I know, but are they connected in parallell pin by pin?

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    Raw Wave tj!2k4's Avatar
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  5. #5
    Constant Bitrate weekendowel's Avatar
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    Didn't really find what I needed. I want to know how the two slots are connected electrically.

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    Raw Wave tj!2k4's Avatar
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    good luck.

  7. #7
    Raw Wave Rob Withey's Avatar
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    Quote Originally Posted by weekendowel
    Didn't really find what I needed. I want to know how the two slots are connected electrically.
    Most signals are parallel. Some have unique pins per slot (eg, IRQ).
    Some bioses have IRQ chaining/sharing support so that a single IRQ can be used for multiple slots. This is motherboard specific.
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  8. #8
    Constant Bitrate weekendowel's Avatar
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    Ok, so this means there could be a difference between motherboards. Maybe I can find some info on VIA web site.

  9. #9
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    If you look at the riser cards that add slots (not just a single slot going horizontal) you'll notice that there's a surface mount chip on the board. Without going into too much detail, some of the PCI signals are slot specific. Meaning, the motherboard associates certain controls lines to specific PCI slots. Each slot is not aware of these other sets of control lines and merely waits for the PCI arbiter chip from the motherboard to allow it to transfer data.

    That extra chip on the riser card is a bridge chip that functions as a "pass-through" PCI device and handles all of these control signal issues locally.

    So, in other words, you can't just "daisy-chain" multiple cards together from one PCI slot. Not all of the signals will be present... not to mention you would have a hell of a headache dealing with trace length issues, clock delays, impedance mismatches, and more.

    The easiest thing is to just buy the riser card and enjoy!

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