Prelab

1. Design and draw the schematic for a 4-bit Adder/Subtractor.
   • Use 4x 1-bit adders rather than a single 4-bit adder and connect the carry-out into the next carry-in
   • Be sure to add an output that will show the result of Carry.
2. The data sheet for the 74LS83 is similar to the 4-bit Logisim adder. Find the datasheet online and use it as a reference.
3. The circuit will perform A+B or A+(-B) to perform subtraction.
   • Remember A-B = A+(-B) = A+ (B +1). where (B + 1) is the 2s complement of B.
4. Create a blank table as shown below to record your prediction and results. Add the rest of the required test cases (3-7).
5. We will test the simulation circuit by doing the following additions & subtractions:
   1. 3 + 2 = 5
   2. 3 - (+2) = 1
   3. 4 + 3 = 7
   4. 3 - (+4) = -1
   5. 5 + 7 = 12
   6. 4 (+4) = -8
   7. 4 + (-4) = -8
6. An example of the chart is shown below:
   • Note that the most significant bit (A3, B3, or S3) act as sign bits, 0 indicating a positive number, 1 indicating a negative number.
   • Be sure to use 2's complement when working with negative numbers, or subtraction.