Lab 2: Hexadecimal Up/Down Counter with ATmega328P

Overview

This project implements a hexadecimal up/down counter using the ATmega328P microcontroller, an 8-bit shift register, a 7-segment LED display, and a pushbutton. All software is written in Assembly language and interfaces directly with the hardware components.

The project satisfies all functionality requirements defined in the Lab 2 assignment for the Embedded Systems course.

Features

• Hexadecimal Counter (0–F)
• Increment/Decrement Mode Toggle
• Counter Reset
• Shift Register Output to 7-Segment Display
• Hardware Debounce Implementation
• Decimal Point Indicator for Decrement Mode

How It Works

Power-On Behavior

• On startup, the display shows 0, and the counter is in increment mode (DP off).

Pushbutton Functions

Button Press Duration	Mode	Action
< 1 second	Increment	Increase counter (0 → F, wraps to 0)
< 1 second	Decrement	Decrease counter (F → 0, wraps to F)
1–2 seconds	Any	Toggle between increment/decrement mode
≥ 2 seconds	Any	Reset counter to 0 (increment mode)

All button actions are triggered on release, and debouncing is handled via a hardware-based approach.

Display

• Counter value is shown on the 7-segment display.
• Decimal Point (DP) indicates current mode:
  • OFF → Increment Mode
  • ON → Decrement Mode

Hardware Components

• ATmega328P Microcontroller
• 8-bit Shift Register (e.g., 74HC595)
• 7-Segment Common Cathode LED Display
• Pushbutton Switch
• Resistors (to limit current to ≤ 6 mA per segment)
• Breadboard and connecting wires

Code Functionality

• Outputs binary values to shift register to light up the correct segments of the display.
• Tracks elapsed time using timer/counter to distinguish between short, medium, and long button presses.
• Manages current state (increment/decrement/reset) and counter value in registers.
• Updates display and DP according to current mode and counter value.

Setup Instructions

1. Connect the ATmega328P to the 74HC595 shift register and 7-segment display following the lab schematic.
2. Wire the pushbutton with hardware debounce (capacitor + resistor circuit).
3. Assemble and upload the Assembly code to the microcontroller.
4. Power the board and test all counter functionalities per the lab instructions.

Mid-Lab Review Expectations

• February 12: Show interaction between MCU and both pushbutton and display. Debouncing should work.
• February 19: Demonstrate increment functionality including wrap-around from F to 0.

Final Submission Requirements

• One .asm source file (this code)
• One lab report per group
• Submit via ICON by February 26
• Checkoff required if being graded in person

Authors

• Thomas Tsilimigras
• Joshua Abello