Term Project $-$ Stopwatch Design

Overview: This project involves designing a digital stopwatch in VHDL that counts from $0$ to $59$ and loops back to $0.$ The stopwatch will output its count using two separate $4-$bit signals: one representing the units digit $(\backslash (0-9\backslash ))$ and the other representing the tens digit $(0-5).$ You will simulate the stopwatch's functionality in ModelSim, demonstrating its behavior based on start and reset controls.

Objectives: The project objectives are as follows:

$-$ Apply modular design principles to implement the stopwatch.

$-$ Create and test components for counting and output control.

$-$ Simulate the design in ModelSim to validate its functionality.

Functional Requirements: To complete this project, you must implement the following core functionalities:

$1.$ Inputs and Controls

$-$ Clock: Use a simulated clock signal in ModelSim to increment the counter.

$-$ Reset: A high $(1)$ signal will reset the stopwatch to $0.$

$-$ Start: When set high $(1),$ the stopwatch starts$/$resumes counting. When low $(0),$ it pauses.

$2.$ Counting Logic

$-$ The stopwatch should count from $0$ to $59,$ then loop back to $0$ and continue counting.

$-$ The counter should increment once per simulated clock pulse.

$3.$ Output Signals

$-$ The stopwatch will have two $4-$bit output signals:

$-$ Units Output $($units$)$: Represents the units digit of the current count $(0-9).$

$-$ Tens Output $($tens$)$: Represents the units digit of the current count $(0-5).$

$-$ For example, if the count is $42$ :

$-$ tens $\backslash (=4\backslash )($binary $0100)$

$-$ units $\backslash (=2\backslash )($binary $0010)$

$4.$ Simulation Requirements:

$-$ Use ModelSim to simulate the design, covering the following test cases:

$-$ Reset operation: Show that the counter resets to $0$ when reset is asserted.

$-$ Start$/$stop operation: Demonstrate that the stopwatch starts counting when start is set high and pauses when it is low.

$-$ Continuous Counting: Verify correct looping from $59$ back to $0.$