1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Question Regarding IC pin numbering and logic gates

  1. Sep 15, 2014 #1
    1. The problem statement, all variables and given/known data
    So I need to assign IC pin numbers to the input and output of the logic gates.

    2. Relevant equations


    3. The attempt at a solution

    I only have limited knowledge on integrated circuits as a whole, so I'm pretty confused altogether. I know that I can hook up inputs and outputs onto my IC, and then produce a result, but how do I know which pin numbers to use?

    Edit: I learned a bit more about integrated circuits and logic gates over the internet, so I understand that each integrated circuit has a built in system of logic gates, and the pins represent either input, output, ground, or voltage source. However, I am still confused about what to do for this, I know that I'll probably be using multiple integrated circuits and using wires to replicate the situation in the picture, but I'm confused about a few things.
    On a breadboard, what exactly is A, B, Cin, S, and Cout?
    Also, is this assignment as simple as I think it is? Just wiring together integrated circuits according to the diagram?
    Last edited: Sep 15, 2014
  2. jcsd
  3. Sep 15, 2014 #2
    Your picture shows a series of logic gates. look up logic symbol images, to see the differences. If you have a specific IC chip in hand that you know has these specific logic gates, then you have to determine which pairs of pins correspond to what types of gates.

    While it has been a while since I played with logic chips, the ones I remember were of a type- one chip was all AND gates, another was OR gates, and so on. if this is the case, you will need a set of chips, then get each ones' pin-out configuration, and that will point you toward the wiring of them.

    As for the letters; while I do cannot know what specifically they refer to in your situation, by the setup, A and B are choices (maybe switches, push buttons, etc) that determine if Cin reaches Cout or S is enabled.

    Reading the logic shown from left to right and top down should enable you to determine what outcome you get for a given input. for example: If you choose ONLY A or ONLY B or ONLY Cin, you get S. any combination of two or three of the options negates that possibility - that comes from the two XOR (exclusive OR) gates at the top. Similarly you can determine what specific set (or sets) of selections allow for Cout to occur.

    Hope this helps, and does not state what you already know. *grin*
  4. Sep 15, 2014 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Logic gates are available in many different forms. Have you been told what family of devices to use or what technology?

    For decades you could/can buy logic gates in "packages" of 2 to 8 gates all of the same type on one chip. A common family is the 7400 series...


    See the table.

    For example a 7402 contains four NOR gates, each having two inputs and one output.

    If you look at the data sheet for it will give you the pin numbers for the inputs and outputs.

    Remember that the inputs of unused (spare) gates should not be left unconnected.

    PS: In general it doesn't matter which of the gates within a package you use. However sometimes you choose one instead of another in order to make the external wiring easier/shorter. For example when connecting the output of one gate to the input of another (of the same type) it helps if they are in the same package and/or the pins are adjacent.
  5. Sep 15, 2014 #4
    Thank you for all your help, combined with my questions to the professor and the knowledge I found on the internet, I successfully completed my task of building a one-bit full adder in the lab. Tons of wires running around everywhere, but I got it done.
    Thanks again.
  6. Sep 16, 2014 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Well done. That's quite a complex "first circuit" to build. I think mine was a lot simpler.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted