MultiSIM ALU Project

Discussion in 'Homework Help' started by Martin65537, Aug 3, 2013.

  1. Martin65537

    Thread Starter New Member

    Aug 3, 2013
    Hello to all!

    I am a first year Electrical engineering student given the task of making a 4-bit ALU capable of 5 functions namely [ADD, SUB, AND, OR, NOT] and I am told to use MultiSIM software to design this.

    So far I have had little problems and I have been able to do the problems after a few days of playing around with it.

    I achieved the first two instructions/opcodes [000 AND, 010 NOT ] by employing 4x 8-1 MUX's.

    The problem I am facing is with the 001 OR opcode. When 001 is supplied to the select lines, the output should be what is on the D1 input right ? However that doesnt seem to be the case in MultiSIM and I havent been able to figure out why..

    I have attached the isolated problem in this topic and I hope someone will be able to point out where I am going wrong.

    I have attached a screenshot of the circuit for those without access to MultiSIM.

    The opcode 001 is for an operation Y = !A OR B. I hope the color schemes are not too difficult on the eyes.

    Also the control G is logic 0 on the input but the line has a NOT gate on it, so it will be logic high when activated.
    Last edited: Aug 3, 2013
  2. Martin65537

    Thread Starter New Member

    Aug 3, 2013
    Update : Figured it out. Turns out the way I wired up C0-C3 was wrong, I wired them up backwards, i.e : 001 would be read as 100 and thus give the wrong output.

    So using the multisim I posted above if you put in 100 in the control lines, it would be read as 001 and thus give the right output!

    Thank you anyway!