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Programming AVR Microcontroller Digital I/O in C

Introduction to AVR Digital I/O C Programming

This AVR tutorial looks at AVR programming for digital I/O in C. Before we start looking at actual programming AVR microcontrollers Digital Input/Output (I/O)recall that each AVR Digital I/O port is associated with I/O registers. Namely the DDRx, PINx and PORTx registers, where x represent the port: A, B, C .....

The DDRx register is use to configure the pins on portx as input or output pins. Each pin on a port is independent and thus the entire port does not have to be configured totally as an input or output port. Writing a 1 in the pin position in the DDRx will configure that pin as an output pin and writing a 0 will configure the pin as an input pin.

Logic values written to the PORTx register is outputted to the pins on Portx that are configured as output pins.

Logic values read from the PINx register is equivalent to the values presently on the pins of Portx which are configured as input pins.

Programming the Digital I/O pins of an AVR in C

The AVR C code below shows how to configure the pins on a port

                 DDRA = 0xFF;       //Configure PortA as an Output port
                 DDRB = 0x00;       //Configure PortB as an Input port
                 DDRC = 0xF0;       //Configure first four pins on PortC as 
                                    //Input pins and the others as output

The AVR C code below shows how to write to or read from the pins of a port once they are configured. Assume here the configurations from the C code above.

                 PORTA = 0xFF;      //Write all 1's to the pins of PortA
                 PORTA = PINB;      //Read values from pins of PortB and 
                                    //write to pins of PortA


Write a program to be downloaded to the Atmel AVR ATMega32 microcontroller which continuously read the logic values on portB and write them to portC.

The program below, written in AVR Studio 5 and AVR Studio 6, accomplish the task that was asked above. There are several things to note here.

  1. The header file avr/io.h must be included in order for us to use the name of the ports.
  2. The ports must be configured before they are used. The first two(2) lines in the main() function of the program are for configuration.
  3. Once the ports are configured you can then write to or read from them, were applicable.
  4. The use of the while(1) loop allows for the continuous read and write operation.
 *  Written in AVR Studio 5 / AVR Studio 6
 *  Compiler: AVR GNU C Compiler (GCC)
 *  Author: AVR Tutorials
 *  Website: www.AVR-Tutorials.com
int main()
	DDRB = 0x00;		//configure portB as input
	DDRC = 0xFF;		//configure portC as output
	return 0;

For another Digital I/O C programming example check out the Interfacing LEDs with the AVR Microcontrollers tutorial.

AVR Tutorials hope this AVR C tutorial on AVR programming for digital I/O was benificial to you and looks forward to your next visit.