Using AVR register

I'm a beginner with Arduino 1.0 software. I want to know if it is possible to use AVR register like DDRA, PINB, ADMUX etc with Arduino 1.0. I try to place DDRA in a programm but when I compile, the message "DDRA was not declared in this scope". If it is possible to place AVR register, could you explain how? Thank you for your help.

Can you post your code? Which board are you compiling for?

I have just add a line ( PORTA = 0;) in the exemple program “blink a led” to test if the AVR register can be use.
The board used is Arduino Uno.
Here is the code :

/*
  Blink
 Turns on an LED on for one second, then off for one second, repeatedly.
 
 This example code is in the public domain.*/


void setup() {                
  // initialize the digital pin as an output.
  // Pin 13 has an LED connected on most Arduino boards:

  pinMode(13, OUTPUT);
  PORTA = 0;              // Add line
}

void loop() {
  digitalWrite(13, HIGH);   // set the LED on
  delay(1000);              // wait for a second
  digitalWrite(13, LOW);    // set the LED off
  delay(1000);              // wait for a second
}

costos: I try to place DDRA in a programm but when I compile, the message "DDRA was not declared in this scope".

Why do you want to?

Where do you see DDRA in the datasheet? Give the page number please.

This compiles:

void setup ()
{
  DDRB = 0;
}
void loop () {}

Result:

Binary sketch size: 468 bytes (of a 32256 byte maximum)

OK, I should have read the ATMEGA328 data sheet before. There is no PORTA! Thank you for your help.