4 bit ALU help

Discussion in 'Homework Help' started by Adame714, May 13, 2018.

  1. Adame714

    Thread Starter New Member

    May 12, 2018
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    Hello there I am trying to create a 4 bit ALU with registers but I am having trouble putting it together.
    I have created ever circuit needed. If someone could point me in the right direct I would greatly appreciate it :)
     
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Welcome to AAC!

    Is this homework?
     
  3. Adame714

    Thread Starter New Member

    May 12, 2018
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    Extra credit
     
  4. dl324

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    For school work, you need to do most of the work. Forum rules only allow members to offer guidance.

    For starters, why are you using registers in an ALU?
     
  5. Adame714

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    May 12, 2018
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    It's required for full credit according to the document I was given.
     
  6. dl324

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    Post the work you've done and the full text of the problem.

    I haven't looked at the RAR file you posted. I don't have any programs installed that can open them...
     
  7. Adame714

    Thread Starter New Member

    May 12, 2018
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    Build a 4 bit CPU using Logisim. We have discussed just about everything you will need for this (Decoders, Multiplexers, Adders /Subtractors, Multipliers, and even some readings on Registers and Memory Cells. There are a few details you may need to readup on, such as: Shifters and Buses (data paths).

    A very base view of a CPU is an Arithmetic Logic Unit, a Controller, Input, output, and Memory. The ALU has a Logical Unit that calculates results for instructions such as AND, OR, NOT, XOR, etc. The Arithmetic Unit is the Adder, Subtractor, etc. The Controller Unit, decodes the instructions and tells the other units what to do. The multiple units of the ALU are feed into a multiplexer and the controller selects the appropriate output.

    Now,you are to create your 4-bitCPU from basic(simple)gates (AND,OR,XOR,NOT,etc). You may NOT use the Logisim’s libraries any of the complex built in circuits.You have to build your allyour own Decoders,Multiplexer etc. With one exception, you may use Logisim’s “D FlipFlop” as handmade latches/flipflop soften have user issues(errors onstartupandoscillation). You may use anything fromt he Wiring,Gate,Input/Output libraries(upper left windowpane of Logisimapplication). So again Logisim’s many built in circuits deciders, Multiplexers,Latches,FlipFlops,Adders,Registers,RAM,etc.areal off limits.If you need a decoder you have to build it from basic gates.



    ArithmeticLogicUnit –A samplecloser towhatyouneedtocreate.A logicunitthatdoesAND,OR, XOR,NOT.Anarithmeticunitanddoesaddition,subtraction,shift(leftandright)compare,increment,decrement,multiplication*. Shiftneed anbitinput for padding value (IusedCarry in).Compare needs toreturn-1,0,1forA<BA=B, A>B respectively.Result(oroutput) is4bits(secondneedfor multiplication) andthe followingflags:Carry,Overflow,Zero, andSign. Inputsare two4bitvalues (A&B),carry-in,andthe op-code(instruction)
     
  8. Adame714

    Thread Starter New Member

    May 12, 2018
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    Here's what I have so far
     
  9. dl324

    AAC Fanatic!

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    A standard 4 bit ALU doesn't use registers; though registers are used in designing a CPU.

    Are you allowed to use datasheets for commercial products? Or you supposed to use truth tables to derive the logic?
     
  10. WBahn

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    Mar 31, 2012
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    You STILL need to show the work you have done so far. We can't help you with problems you are having if you won't do that.

    The first thing is to make sure that YOU know exactly WHAT it is you are trying to accomplish. Exactly what does this ALU need to be able to do. Don't just parrot some generic verbiage, list EXACTLY what it needs to do.

    EDIT: Cross posted with TS's post of work so far.
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    You've got a number of blocks that have no label, either for the pins or for the block as a whole. No way to know what is going on there.

    Also, we can't even begin to guess if what you have is even close to what you need until you are able to list exactly what you need.
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    MOD NOTE: Moved to Homework Help.
     
  13. KeepItSimpleStupid

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    Mar 4, 2014
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