Revision as of 11:22, 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

FIODIR:Fast GPIO Direction Control Register.
This register individually controls the direction of each port pin.

FIOSET:Fast Port Output Set Register.
This register controls the state of output pins. Writing 1s produces highs at the corresponding port pins. Writing 0s has no effect. Reading this register returns the current contents of the port output register not the physical port value.

FIOCLR:Fast Port Output Clear Register.
This register controls the state of output pins. Writing 1s produces lows at the corresponding port pins. Writing 0s has no effect.

FIOPIN:Fast Port Pin Value Register.
This register is used for both reading and writing data from/to the PORT.
Output: Writing to this register places corresponding values in all bits of the particular PORT pins.
Input: The current state of digital port pins can be read from this register, regardless of pin direction or alternate function selection (as long as pins are not configured as an input to ADC).
Note:It is recommended to configure the PORT direction and pin function before using it.

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.