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Wide Logictranceivers with Hysteresis

Discussion in 'Electronic Design' started by Uwe Bonnes, Sep 10, 2007.

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  1. Uwe Bonnes

    Uwe Bonnes Guest

    While e.g. TI explicitly mentions and specifies Input hysteresis for the
    SN74LS245, for newer families the keyword "hysteresis" is only mentioned for
    the real "schmitt-triggers" (14,17,132). The part with most gates in a
    package is the 74xx14 with 6 gates, however with a non-flow-through layout.

    Do you know any good available 8/16/.. Bit wide logictranceiver with
    flow-through layout in a modern logicfamily like LVC?

    Thanks
     
  2. Joerg

    Joerg Guest

    I just designed one in, 74LVC244:
    http://www.nxp.com/acrobat_download/datasheets/74LVC_LVCH244A_4.pdf

    The NXP datasheet explicitly states "Schmitt-trigger action at all
    inputs" while TI doesn't. So I had the unfortunate situation of
    releasing one mfg and not another. But don't expect much detail even
    from the NXP datasheet, it ain't like in them good old days no more.

    Hey, my design-in rate for NXP now went from 0% to 0.1%! Despite the
    fact that they seem unable to design a good web site.
     
  3. Uwe Bonnes

    Uwe Bonnes Guest

    No specification about the hysteresis and no tranceiver, but thanks
    for the pointer (and I remember you mentioned the part in a similar thread
    that my search keywords didn't bring up...).
    Bye
     
  4. Joerg

    Joerg Guest

    Well, I use it as a transceiver (back-to-back). It's fairly easy because
    they split them in half. As for the hysteresis, as I said, specsmanship
    ain't what it used to be. However, Philips always had excellent family
    specs so you might want to look those up. As long as NXP hasn't blown
    the access to that.

    Chances are there may not be a Schmitt transceiver with layout-friendly
    pin-out and a defined hysteresis level. Or as they say in Germany you
    might have to bake one ;-)
     
  5. Uwe Bonnes

    Uwe Bonnes Guest

    I already considered to use the XC2C32A in 44-VQFP package. You can program
    the Input for 500mV Hysteresis, Bus-Hold, Pullup or none. At [email protected] pieces
    comparable to a SN74LVC16245ADGGR at [email protected], disregarding the need for the
    1.8 volt supply.

    At least
    module transceiver (
    inout [15:0] busa,
    inout [15:0] busb,
    input dir
    );
    assign busa = (dir)? busb: 16'bz;
    assign busb = (dir)? 16'bz: busa;
    endmodule

    fits in the XC2c32a and implements a 16 bit transceiver with Direction
    input.

    I wonder why so few modern logic series offer hysteresis as inputs option.

    Cheers
     
  6. Joerg

    Joerg Guest

    That is what I have wondered about since the start of my career. I mean,
    it ain't rocket science to implement it. I was never fond of
    programmables. The first ones (PALs) were extremely inefficient when it
    came to power consumption while the newer ones are typically
    single-sourced and have rather short production life spans.
     
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