When we start programming microcontrollers, it’s important to understand the basic structure of the C program used to control hardware devices. The AVR microcontroller uses a very organized and simple structure that follows the standard C programming pattern but also includes some special header files for hardware access. The structure defines how the program begins, executes, and repeats operations endlessly to control LEDs, sensors, or motors. It consists mainly of header files, the main function, variable declarations, initialization of ports, and the logic of the program inside an infinite loop. Writing a well-structured AVR C program not only helps in easier debugging but also improves portability between different AVR devices. Before writing large and complex programs, one must clearly understand the basic structure of an AVR C program, which acts as the foundation for all embedded projects. In this article, we’ll explore the essential parts of an AVR program, learn what each section does, and finally see a practical example.
Basic Structure of an AVR C Program
Every AVR program in C language begins with including necessary header files, followed by defining global variables or macros, then the main function which contains the operational code. The main function is the entry point of the program and runs continuously as long as the microcontroller is powered on. A simple structure of an AVR program is shown below:
#include <avr/io.h> // For Input/Output register definitions
#include <util/delay.h> // For delay functions
int main(void) {
// Step 1: Port Direction Setup
DDRB = 0xFF; // Set PORTB as Output
// Step 2: Infinite Loop for Execution
while(1) {
PORTB = 0xFF; // Turn ON LEDs
_delay_ms(500); // Wait 500ms
PORTB = 0x00; // Turn OFF LEDs
_delay_ms(500); // Wait 500ms
}
}
Explanation of Each Section
The AVR program can be divided into four important sections — Header Files, Global Declarations, Main Function, and Infinite Loop. Each section plays a specific role in the program flow.
| Section | Description |
|---|---|
| Header Files | These files contain definitions of registers, macros, and functions that simplify hardware access.
For example, <avr/io.h> provides register names like PORTB, DDRB, etc., while <util/delay.h> gives delay functions. |
| Global Declarations | Here, global variables, macros, or constant values are defined.
These values are accessible throughout the program. Example: #define LED 0x01. |
| Main Function | This is where the execution begins.
Inside the main() function, we set port directions (input/output), initialize peripherals, and write control logic. |
| Infinite Loop | The while(1) loop ensures the program runs continuously as long as power is ON.
This is necessary for embedded systems since they don’t “exit” like normal computer programs. |
Program Flow Diagram
Points to Remember
- Always include
<avr/io.h>before using register names like PORT or DDR. - Use
_delay_ms()and_delay_us()functions only after including<util/delay.h>. - Never leave the main loop empty; it must continuously run the control logic.
- Comment your code for better readability and maintenance.
Conclusion
The basic structure of an AVR C program defines the foundation of all embedded programming. By understanding how to organize code, include header files, and design the main function with an infinite loop, we can easily move on to advanced topics like timers, ADC, and communication protocols. A clean and structured program makes debugging easier and ensures better hardware control. Once this basic structure is clear, writing any embedded program becomes a smooth and enjoyable process.
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