Skills Overview

Software: Quartus Prime, ModelSim

Hardware: DE1-SoC Board

Core Concepts: Arithmetic Logic Units (ALUs), 2's Complement, Signed Arithmetic, Overflow Detection, Modular Design.

Technical Overview

• Signed Arithmetic: The ALU performs addition and subtraction on 4-bit signed numbers. Subtraction is achieved by converting the subtrahend to its 2's complement form (inverting each bit and adding one) before the addition.

• Modular Design: The core of the ALU is a 4-bit adder, which was built by first designing a 1-bit full adder and then connecting four instances together structurally.

• Opcode Control: A control input allows the user to select one of four distinct operations: Add X to Y, Add 1 to X, Add 0 to X, or Subtract Y from X.

• Negative & Overflow Handling: The design incorporates a sign bit to trigger a negative symbol on the display for negative results. It also includes dedicated logic to signal an overflow condition with an LED if the result exceeds the 4-bit signed range.

Key Concepts on Display

Mux Components

Adder Components

Top Level Components

Board Demos

1 Bit adder Logic Worked Out 

Additional Comments

A primary challenge during this project was correctly distinguishing between the binary representation of a valid negative number and a true arithmetic overflow. Resolving this issue led to a deeper understanding of the underlying logic of 2's complement arithmetic. The result was a functional and reliable circuit that accurately performs addition and subtraction while correctly accounting for edge cases like negative results and overflows.

(Additionally, such components such as the logic surrounding the sign bit display is not showcased on this page due to it being simple check of wether subtraction was selected and if no overflow was detected, is both happen a negative number would have occured that resulted in specifically a negative number)