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Basic vs. High Speed Wallace Tree

Discussion in 'Electronic Basics' started by logjam, Feb 19, 2006.

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  1. logjam

    logjam Guest

    Yeah, I know this part probably hasn't been sold in the past 15 years,
    but I can't figure out the data sheet.

    The 74S275 Wallace tree has 2 versions. The high speed and basic. In
    the high speed version, both C2n inputs are grounded and the carry bit
    is passed through 2n+0 to an external adder. I don't understand why
    this makes it "high speed" since there is supposed to be an adder
    already inside the 275. Is it a "high speed" version because the built
    in adders are junk? Or because the built in adders have to pass through
    gated buffers?
     
  2. I haven't been able to find the data sheet on the '275. I have some
    older data books (1988), but obviously not old enough. I may be able
    to find my 1970's, nicely bound TI version... but it's probably in
    boxes somewhere.

    In any case, it turns out that:

    C.S. Wallace, "A Suggestion for A Fast Multiplier," IEEE Transactions
    on Elec. Computers, vol. EC-13, pp. 14-17, (Jan or Feb) 1964.

    and,

    Y. Ofman, "On the algorithmic complexity of discrete functions," Sov.
    Phys. Dokl. 7.7, pp. 589-591, 1963.

    Spring to the fore on the subject.

    Try a google search using:
    wallace "A suggestion for a fast multiplier" filetype:pdf

    Some hits are:
    http://www.iccd-conference.org/proceedings/1998/90990122.pdf
    http://www.ceet.niu.edu/faculty/reza/articles/iscas2002.pdf
    http://www.ece.ucsb.edu/Faculty/Parhami/pubs_folder/parh99-asilo-opt-depth-circ.pdf
    http://wwwmaths.anu.edu.au/~brent/pd/rpb055.pdf

    You might like this one:
    http://www.eecs.berkeley.edu/Pubs/TechRpts/2003/CSD-03-1288.pdf

    Jon
     
  3. Or maybe that is:

    Y. Ofman, "On the Algorithmic Complexity of Discrete Functions," Dokl.
    Akad. Nauk SSSR 145:48–51, 1962.

    Something like those, anyway. I haven't read it, of course. My wife
    knows a little Russian, but I know absolutely none. Just German.

    Jon
     
  4. logjam

    logjam Guest

    Here is a link to the datasheet from 1975:
    http://www.tech-systems-labs.com/booksdata/TI-DATA-1976.pdf

    Take a look at page 7-395

    I'll take a look at a few of those links. I think the difference
    between high speed and standard wallace tree isn't that the wallace
    tree itself is slow but that since the 275 is 3 state using buffers it
    might make carry propagation slightly slower. The high speed tree is
    56ns and low speed 90ns, so I just can't understand how the buffers
    could slow it down that much (unless the 1bit adders in the 275 are
    junk).


    Since the 486 requires 13-42 cycles to unsigned multiply mem32, at
    50MHz my 5MHz TTL computer might actually be faster ant the 486. :)
    BUT, my NOP and MULU take the same amount of time. So the 486 50MHz
    gets 50 MIPS NOPping. :)
     
  5. logjam

    logjam Guest

    Yep. The whole '75 data book! :)
     
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