CS2110 -Timed Lab 1 -Arithmetic Logic Units - Solved

In this timed lab, you will be creating an ALU with four operations. This ALU will take in two 8-bit inputs and one 2-bit op code. It will output one 8-bit output.

2.1         Tasks and Strategy
•             Set up your MUX for the ALU output.

•             Build your first operation circuit, and connect it to the MUX. 

•             Build your second operation circuit and connect it to the MUX. 

•             Rinse and repeat (do operations 3 and 4). • Hint: After you complete each operation, you may want to save a local copy of your file as a backup. That way, if you have a problem later on, you can revert to the prior working version quickly.

2.2         Allowed Components
When building this ALU, you may only use:

1.       basic logic gates (AND, OR, NAND, NOR, NOT, XOR),

2.       decoders,

3.       multiplexers,

4.       the built-in Circuitsim adders (NOT the built-in subtractors),

5.       splitters,

6.       wires,

7.       tunnels,

8.       constants,

9.       input pins,

10.   output pins

IMPORTANT NOTE 1: YOU DO NOT NEED TO BUILD THE GATES OUT OF TRANSISTORS. PLEASE, FOR YOUR OWN SAKE, DON’T DO IT. USE THE BUILT IN GATES.

IMPORTANT NOTE 2: You’re allowed to use CircuitSim’s default, built-in adders (in the Arithmetic tab). So please don’t try to make your own adders, just use that one. You’re not allowed to use anything else from the Arithmetic tab (don’t try to use a subtractor; if you need a subtractor, you will need to create your own using the above-mentioned components).

3           Instructions
3.1         CircuitSim Information
For this assignment, you will be using CircuitSim. The version is the exact same as the one used in Homework 2 and 3, and can be found on the Docker image provided for this class. To ensure you are on the correct version, check to see if the title bar says ”CircuitSim v1.8.2 2110 edition”. If your file does not open in this version of CircuitSim you will receive a 0. All changes should be made in the tl1.sim file. Do not move or rename any or the input or output pins.

3.2         ALU Components
You will create an 8-bit ALU with the following operations, using any of the gates listed above. All numbers should be interpreted as 2’s complement.

00. (A − B) / 2
[(A - B) / 2]
01. signOfB
[B < 0 return -1, B == 0 return 0, B > 0 return 1]
10. merge
[Ex. A = 00000000, B = 11111111, output = 00001111]
11. logicalImplies
[A -> B, see truth table below for more information]
Below are descriptions to elaborate more on the problems above. If you’re still struggling to comprehend what the question is exactly asking after reading below, please ask one of your TAs for clarification.

•    In the (A - B) / 2 operation, note that for (A - B), the test cases will ALWAYS have an even number as a result of this operation. Also, overflow from (A - B) is not to be mitigated in any way. For example, for (-100 - 50) / 2, the answer will NOT be -75. Rather, it would be (-100 - 50) / 2 = (106) / 2 = 53.

•    For the signOfB operation, you need to return the sign of B. If B < 0, as in if B is negative, return -1. If B == 0, return 0. If B > 0, as in B is positive, return 1.

•    Notice that signOfB depends solely on the B input. It should NOT rely on A being a particular value.

•    merge should return an output where the 4 most significant bits (leftmost bits) correspond to the 4 most significant bits of A, and the 4 least significant bits (rightmost bits) correspond to the 4 least significant bits of B. For example, if A = 10111111 and B = 01011010, the output should be 10111010. In the output, the first 4 bits 1011 are from A, and the last 4 bits 1010 are from B.

•    For the logicalImplies operation, you’ll be implementing the logical implication table, which has been included below for reference. You should apply this operation to all 8 bits using A and B.

A
B
Output
0
0
1
0
1
1
1
0
0
1
1
1
•    This ALU has two 8-bit inputs for A and B and one 2-bit input for OP, the op-code for the operation in the list above. It has one 8-bit output named out.

•    The provided autograder will check the op-codes according to the order listed above (A − B) / 2 (00), signOfB (01), etc.) and thus it is important that the operations are in this exact order.