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PCI 5V Interface

Jesus Ortiz
Prodigy 120 points
Other Parts Discussed in Thread: PCI2250

Hi,

I have to implement a PCI interface with a Xilinx Spartan-6 FPGA for a legacy product (PCI universal add-in board). As that FPGA is not 5V tolerant, I have to add an interface between it and PCI connector (5V and 3V3 compatible) in order to bidirectionally translate voltage levels.

I think I have two possible solutions:

  • On the one hand, the PCI bridge PCI2250. But since I'm going to use it as a simple interface (not as a real bridge, because there's not going to be a secondary PCI bus in the add-in card), I suppose that chip is too much for what I really need.
  • On the other hand, SN54CBT16244, wich has a CON lower than 10 pF. But I'm not really sure about whether this option would be appropriate or not (PCI compliant).


Any idea about this? Would the PCI2250 option be the best of all? Or is there any voltage translator or any other chip more suitable for this application?

Thanks in advance

Regards
Jesus

  • 0
    TI__Mastermind 45350 points
    Jesus,

    I will check to see if the SN54CBT16244 is PCI compliant. If it is not I will also look at other translations options.

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    TI__Mastermind 45350 points
    Jesus,

    I cannot find a reason why the SN54CBT16244 cannot be used in your application. Were there any performance issues you were concerned about?

    Thank you,
    Adam
  • 0 in reply to Adam Torma
    Prodigy 120 points

    Hi Adam,

    According to point "4.1 CBT and CBTD Devices" in Texas' Application Report, SCEA035A - June 2004 "Selecting the Right Level-Translation Solution":

    Devices from the CBT and CBTD families can be used to interface 5-V systems with 3.3-V systems. These devices can only be used to down-translate when interfacing a 5-V CMOS system with a 3.3-V system. They can be used for bidirectional translation when interfacing a 5-V TTL system with a 3.3-V system.

    Since I need bidirectional translation and PCI is a CMOS bus, I wasn't sure whether SN54CBT16244 option would fit my requirements or not. That is my concern.

    Thanks

  • 0 in reply to Jesus Ortiz
    TI__Genius 9860 points

    Hi Jesus, the CBT device has an output limited to VCC - 1 V. But you can pull up the output to 5 V because the outputs will go high impedance once the input passes VCC - 1 V.

     

  • 0 in reply to C. Ryan Land
    Prodigy 120 points

    Hi Ryan,


    I'm afraid I can't use pull-up resistors on PCI side (5V environment) since the attach of any pull-up resistors in PCI add-in cards would be specifically a violation of PCI specification.

    Anyway, regarding PCI 5V environment, I have recently found out that it is compatible with TTL switching levels. So, although I'm going to have a high level voltage of 2,8-3V, it will be fully functional, since the TTL limit is 2V for high levels.

    Thanks for your support

    Regards