Unit #4-20

Learning Outcome

At the end of this lesson, you will be able to:

  • build a 2-bit full adder/subtractor


  • go over two compliment subtraction


  • remember, to subtract a twos compliment number, flip every bit and do addition, plus add 1.
  • we know how to flip every bit, it is called a NOT gate
    • if you want to flip or not, you can use an XOR gate
      • Bit, control and output


  • nil

Daily Assignment

  • circuit - "2-bit full Adder/subtractor"
    • add the XOR and carry in bit to the control and create a full adder/subtractor
    • DO NOT do the normal Fritzing diagram
    • join with another student if you want to (they already have a full adder!)
    • just ground your Carry In, so that it is always zero
  • build the circuit on your breadboard
    • once working, call me over to check
    • take a picture of your completed breadboard and upload it to your notebook
  • Note: you should be uploading 2 things to your notebook:
    1. truth table
    2. picture of completed real world breadboard


    • if you finish early, move to next circuit