1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

binary subtraction using 2's complement

Discussion in 'Mathematics and Physics' started by tejasvi, Feb 9, 2018.

  1. tejasvi

    tejasvi New Member

    Joined:
    Jun 18, 2009
    Messages:
    9
    Likes:
    0
    how do i calculate binary subtraction of 0000-0001 using 2's complement
    my calculation looks like this
    0001 >complement= 1110 > adding 0001 = 1111
    finally adding it to
    0000
    1 1 1 1
    -------
    1 1 1 1 which is wrong

    but in reverse i get correct answer
    0000 >complement= 1111 > adding 0001 = 0000
    0000
    0001
    -------
    0001 which is correct
     
  2. Ian Rogers

    Ian Rogers User Extraordinaire Forum Supporter Most Helpful Member

    Joined:
    Mar 28, 2011
    Messages:
    9,827
    Likes:
    961
    Location:
    Rochdale UK
    1111 is -1...

    0011 = 3
    0010 = 2
    0001 = 1
    0000 = 0
    1111 = -1
    1110 = -2
     
  3. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,423
    Likes:
    600
    Location:
    AZ 86334
    Are you asking " how do I form the twos complement of an integer?", or "how do I do subtraction using twos complement?"
     
  4. dave miyares

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    2
    Likes:
    -10


     
  5. Ratchit

    Ratchit Well-Known Member

    Joined:
    Mar 12, 2008
    Messages:
    2,058
    Likes:
    98
    No it's not. You don't understand 2's complement arithmetic. 1's complement arithmetic has a plus zero (0000) and a negative zero (1111). 2's complement arithmetic has only a positive zero (0000). Therefore, 1111 represents -1 decimal in 2's complement arithmetic and your answer is correct.

    Why are you puzzled when you get a positive one when you add zero to a positive one?

    Ratch
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

    Joined:
    Oct 30, 2010
    Messages:
    10,176
    Likes:
    1,126
    4 bits in 2's complement would represent -8 to +7. 16 bits represents -32768 to 32767; there is only one zero in 2's complement notation.

    The left most bit is the sign bit and you can "sign extend" that. so if you had 1111 (-1) sign extended to 16 bits 1111 1111 1111 1111 is still -1.
    So is 0001 (1) sign extended to 16 bits 0000 0000 0000 0001 is still 1.
     
    • Like Like x 1

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice