Revision as of 11:41, 4 February 2016

Bagwan (talk)

Objective

In this tutorial we are going to discuss the port configuration of AVR/Atmel controllers or in general Atmega family. In this tutorial we will be using Atmega32 as reference, same will be applicable to other Atmega series controllers.

At the end of this tutorial you will be familiar with the Atmega GPIO's and the associated registers for configuring and accessing the GPIO's.

GPIO Registers

The basic and important feature of any controllers is the number of gpio's available connecting the peripherals. Atmega32 has 32-gpio's grouped into four 8-bit ports namely PORTA-PORTD as shown in the below image.

As shown in the above image many I/O pins have 2-3 functions. If a pin is used for other function then it may not be used as a gpio.

Though the gpio pins are grouped into 8-bit ports they can still be configured and accessed individually.
Each Port is associated with 3 registers for direction configuration(Input/Output), read and write operation.

DDRx: Data Direction Register
Before reading or writing the data from the ports, their direction needs to be set. Unless the PORT is configured as output, the data from the registers will not go to controller pins.

This register is used to configure the PORT pins as Input or Output. Writing 1's to DDRx will make the corresponding PORTx pins as output. Similarly writing 0's to DDRx will make the corresponding PORTx pins as Input.

DDRB = 0xff;  // Configure PORTB as Output.
 
DDRC = 0x00; // Configure PORTC as Input.
 
DDRD = 0x0F; // Configure lower nibble of PORTD as Output and higher nibble as Input
 
DDRD = (1<<PD0) | (1<PD3) | (1<<PD6); // Configure PD0,PD3,PD6 as Output and others as Input

PORTx:
This register is used to send the data to port pins. Writing 1's to PORTx will make the corresponding PORTx pins as HIGH. Similarly writing 0's to PORTx will make the corresponding PORTx pins as LOW.

PORTB = 0xff;  // Make all PORTB pins HIGH.
 
PORTC = 0x00; // Make all PORTC pins LOW..
 
PORTD = 0x0F; // Make lower nibble of PORTD as HIGH and higher nibble as LOW 
 
PORTD = (1<<PD0) | (1<PD3) | (1<<PD6); // Make PD0,PD3,PD6 HIGH,

As all the Atmega Ports and SFR's(Special Function Registers) are defined in io.h, this has to be included at the beginning of the project/code.