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7402 vs. 74L02 vs 74LS02 for Altair Clone

Discussion in 'Electronic Basics' started by logjam, Jan 8, 2006.

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  1. logjam

    logjam Guest

    Can someone explain the main differences between those 3 families of
    logic chips?

    I read "standard TTL inputs are stable floating, will read high" and
    that "you can't substitute modern TTL families for standard and expect
    some old equipment to work"

    A project I am working on right now is duplicating an Altair 4k DRAM
    board. I'm preparing to place an order for the ICs. The manual calls
    for 74L02, 74LS00, and a 7406 (for examples). Did they choose these
    different styles (L vs. LS vs. 'nothing') because of cost or were they
    really necessary?

    The manual (link included below) is GREAT. I wish all manuals could be
    this great. :) Not really...

    For example Rev.0 of the board had a IC A, B, R as 74L04s and Rev2
    changes B to an LS04.
    Rev0 has a 7420 for J and rev2 has an L20.
    Revo has a 7400 for L and K, rev2 has a 74LS for L and a 74L00 for K.

    I suppose this could be due to wiring...

    Do I really need to be this specific when ordering new logic chips?

    I'm wondering if I need to special order these parts or if some of them
    will interchange. Will an LS part work in place of an L, or L in place
    of a 'nothing': LS work in the place of a nothing? Do you have any
    suggestions on how I could find information on these old parts?
    Searching in google only results in old stock results.


    Here are 300dpi scans of the board and a datasheet in case you are
    interested.

    If you're interested in my Altair duplication project send me an e-mail
    and I'll keep you updated.

    1975 4k DRAM kit:
    Top Assembled - http://www.stockly.com/images2/060108-75_Front.jpg
    Top Bare - http://www.stockly.com/images2/060108-75_Front_Bare.jpg
    Bottom Bare - http://www.stockly.com/images2/060108-75_Back_Bare.jpg
    Manual -
    http://www.stockly.com/images2/060108-75-Card_Docs-88-4kdra.pdf
     
  2. Marky

    Marky Guest

    74 was the original chip series.
    74L was the low power series
    74LS was the low power cmos series.

    And thats without googling. ( but I may be wrong )

    I would just use what was cheapest, but trying to get the LS if possible
    because of
    the lower power usage.
     
  3. Sjouke Burry

    Sjouke Burry Guest

    74lsxxx is low power scottky (no cmos!!!!)
     
  4. Rich Grise

    Rich Grise Guest

    ^^^^

    Low Power Schottky.

    74S is the Schottky series, very fast, but very high power consumption.
    74LS melded the "L" series with the "S" series, and came up with low
    power, but fast, chips - mostly they replaced standard TTL (the 'nothing'
    series), because they worked at the same speeds at dramatically less
    power.

    74C is the CMOS series, relatively slow, but almost no power consumption,
    74HC is the high-speed CMOS series, really low power consumption at idle,
    but with mongo output drivers, ("High-Power CMOS", if that's not an
    oxymoron.[1])

    74HCT is the high-speed CMOS series with TTL-compatible inputs. (HC
    outputs are practically rail-to-rail, so there's no problem with them
    driving practically anything, except maybe ECL, but that's a whole nother
    ball game...)
    Oh, yes, Not googling is always wrong. Shame on you. >:-[
    - ;-) <- [smiley means, "don't take that last line too seriously." But
    _do_ google. :) ]
    Or if you want to drag yourself kicking and screaming into the 21st
    century, you could look into HCT or even ACT. ;-P

    Cheers!
    Rich
    [1] I have no idea where that word came from, and frankly, it sounds like
    pimple cream for retarded people. ;-P
     
  5. Hello from the Constant Timelord
    No. 74LS was the Lowpower Schottky version of the SN74 series of devices. You
    are thinking of 74C which both TI and NSC made.
    -
    Gregg drwho8 atsign att dot net
    "This signature is always right."
     
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