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Adding bytes with 4-bit full adders

  1. Apr 25, 2007 #1
    hi guys...my question is kinda weird..

    i want to add 1 byte to another 1 byte and get the result on 7-segments :grumpy:
    i have to use the ICs 74283 (4- bit full adder)... and i no how to connect them to add 1byte + 1 byte

    but i am still lost on how to get the output on 7segments !!!

    would i have to make a truth table to each input to the three 7segments in parallel
    but that would take me for ever..
    i am just kinda lost :S
  2. jcsd
  3. Apr 25, 2007 #2


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    You'll need to use two 4-bit full adders to make an 8-bit full-adder, connecting their carry bits as necessary.

    To create a 7-segment decoder, create a truth table and use a Karnaugh map to reduce it into simple gates. Chips already exist which perform this decoding, if you're allowed to use them.

    - Warren
  4. Apr 25, 2007 #3

    i am already passed through the two 4-full adder IC
    and the doctor just left it up to us the whole project....

    but chroot this way i think i am gonna use three 7 segments...coz if the input is (11111111) on each input the out put would be 254 in binary...

    so am i gonna make truth table for 254 output??

    Last edited: Apr 25, 2007
  5. Apr 25, 2007 #4


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    Was your project to do BCD (binary to decimal conversion)?
    In which case you would need three 7 segments.

    With a little creativity you can show standard hex notation on a 7 segment display.
  6. Apr 25, 2007 #5
    my project was to add 2bytes using 4-full bit adder and have the output on 7-segments...

    and for the Hex decimal.. i thought of that but i found that i would also need 3 7 segment...
    but it doesnt matter
    it can go either way
  7. Apr 25, 2007 #6
    Ya, thats exactly what our professor said (I'm Duellist's class-mate, and partner in this project :rolleyes: )

    I'm just so confused as to what we have to do in this project.. Ok, I know the part where we have to use two 4-bit full adders in order to add the bytes together, but how will we connect the 7-segment displays? Check this picture out:


    The question is "where do the outputs go in order to display it on 7-segment display(s)" =D ... Btw chroot (or Warren), we do use the decoders, the 7447's...

    Last edited: Apr 25, 2007
  8. Apr 25, 2007 #7


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    Well, the 7447 is a BCD-to-seven-segment decoder, so you'll first need to convert your sum from binary to BCD. BCD decoders are very simple, so you should be able to design them from discrete gates pretty easily. Since you're allowed to use the BCD-to-seven-segment decoder, perhaps you're allowed to use existing binary-to-BCD chips, too?

    - Warren
  9. Apr 26, 2007 #8
    ya i think we are allowed some kind of the decoders chips....

    but wat do u have in mind?

  10. Apr 26, 2007 #9
    I never knew there were binary-to-BCD decoders, lol... Ok, so now i get it...

    Outputs from the two 4-bit full adders >into> binary-to-BCD decoder >into> BCD-to-7 segment decoder...
  11. Apr 28, 2007 #10
    hi its me again
    let me ask u sth
    is there's any kind of decoder that would get 4-bit and would convert them to hex decimal...
    it would actually help.....
    i mean take the binary 1001 and say 9 and when it has 1111 it present F
    that would make everything actually helpful

  12. Apr 29, 2007 #11


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    It's possible to display A,b,C,d,E,F on a 7 seg.
    I recall some 7447 (or equivalent) chips did just that for the hex A-F bit patterns.
    Depended on the manufacture.
    You would need to examine datasheets.
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