avr programming

Introduction to AVR

ProgrammingApplied Electronics (28846)

Fall 2014

Ali Shayei 1

Sharif University of

Technology

Block Diagram and

Pin Configurations

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Fuse Bits

There are few parameters in the chip which are used toconfigure it before it can be used for externalenvironment. These parameters are set with the use ofFuse Bits.

Once the fuse bits are set for a particular configuration,the controller can be used again and again

You dont have to set the fuse bits every time you are usingthe controller till the time you want to use it under thesame configuration.

Fuse bits need to be changed only in case you want tochange the initial configuration of the controller.

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System Clock and Clock Options

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Device Clocking Options Select

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The Clock Source is determined by CKSEL fuse bits

5

Input/Output Ports

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I/O Ports and

The communication channels

through which information

flows into or out of the

microcontroller

Example: PORTB

Pins PB0 PB7

May not be contiguous

Often bi-directional

C

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Port Pin Data Directionality

Input

When you want to take information from the external world

(sensors) into the MCU

Output

When you want to change the state of something outside the

MCU (turn a motor on or off, etc.)

Pins default to input direction on power-up or reset

Your program can set or change the directionality of a

pin at any time

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Setting the Pin Data Direction

Each port pin consists of three register bits: DDxn, PORTxn, and PINxn. the

DDxn bits are accessed at the DDRx I/O address, the PORTxn bits at the PORTx

I/O address, and the PINxn bits at the PINx I/O address.

The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is

written logic one, Pxn is configured as an output pin. If DDxn is written logic

zero, Pxn is configured as an input pin.

If PORTxn is written logic one when the pin is configured as an input pin, the

pull-up resistor is activated. To switch the pull-up resistor off,PORTxn has to be

written logic zero or the pin has to be configured as an output pin. The port

pins are tri-stated when reset condition becomes active, even if no clocks are

running.

If PORTxn is written logic one when the pin is configured as an output pin, the

port pin is driven high (one). If PORTxn is written logic zero when the pin is

configured as an output pin, the port pin is driven low (zero).Ali Shayei 9

Setting the Pin Data Direction

Traditional Coding

DDRB = 0x3F

PORTB = 0x2F

Arduino

pinMode(pin_no., dir)

Ex. Make Arduino pin 3 (PD3) an output

pinMode(3, OUTPUT);

Note: one pin at a time

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Pin Voltages

Microcontrollers are fundamentally digital devices. For digital IO pins:

Information is coded in two discrete states:

HIGH or LOW (logic: 1 or 0)

Voltages

TTL

5 V (for HIGH)

0 V (for LOW)

3.3 V CMOS

3.3 V (for HIGH)

0 V (for LOW)

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Pin Used as an Output

Turn on an LED, which is connected to pin Arduino

pin 0 (PD0) (note the resistor!)

What should the data direction be for pin 0 (PD0)?

pinMode(___, ______);

Turn on the LED

digitalWrite(___,______);

Turn off the LED

digitalWrite(___,______);

ATmega328

Arduinopin 0(PD0)

0 OUTPUT

0 HIGH

0 LOW

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Pins as Inputs and Pull-up Resistors

Using a switch as a sensor

Ex. Seat belt sensor

Detect the switch state

What should the data direction be for Arduino pin 3 (PD3)?

pinMode(__, ______);

What will the voltage be on PD3 when the switch is closed?

What will the voltage be on PD3 when the switch is open?

Indeterminate!

ATmega328

Arduinopin 3(PD3)

3 INPUT

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Pins as Inputs and Pull-up Resistors

Switch as a sensor, cont.

Make the voltage on the pin determinate by turning

on the pull-up resistor for PD3

Assuming PD3 is an input:

digitalWrite(3,HIGH); turns on

the pull-up resistor

pinMode(3,INPUT_PULLUP);

What will the voltage on PD3 be when the switch is

open?

VTG

What will the voltage on PD3 be when the switch is

closed?

ATmega328

PD3

VTG= +5V

0

1

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Example 1

Arduino approach

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Alternate approach

Make Arduino pins 3, 5, and 7 (PD3, PD5, and PD7)

to be outputs

pinMode(3, OUTPUT);

pinMode(5, OUTPUT);

pinMode(7, OUTPUT);

DDRD = 0b10101000;

or

DDRD = 0xA8;

or

DDRD | = 1

Example 2

Arduino approach

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Alternate approach

Make pins Arduino pins 0 and 1 (PD0 and PD1)

inputs, and turn on pull-up resistors

pinMode(0, INPUT_PULLUP);

pinMode(1, INPUT_PULLUP);

digitalWrite(0, HIGH);

digitalWrite(1, HIGH);

DDRD = 0; // all PORTD pins inputs

PORTD = 0b00000011;

or

PORTD = 0x03;

or better yet:

DDRD & = ~(1

Structure of an Arduino Program

An arduino program == sketch

Must have:

setup()

loop()

setup()

configures pin modes and registers

loop()

runs the main body of the program forever

like while(1) {}

Where is main() ?

Arduino simplifies things

Does things for you

/* Blink - turns on an LED for DELAY_ON msec,

then off for DELAY_OFF msec, and repeats

BJ Furman rev. 1.1 Last rev: 22JAN2011

*/

#define LED_PIN 13 // LED on digital pin 13

#define DELAY_ON 1000

#define DELAY_OFF 1000

void setup()

{

// initialize the digital pin as an output:

pinMode(LED_PIN, OUTPUT);

}

// loop() method runs forever,

// as long as the Arduino has power

void loop()

{

digitalWrite(LED_PIN, HIGH); // set the LED on

delay(DELAY_ON); // wait for DELAY_ON msec

digitalWrite(LED_PIN, LOW); // set the LED off

delay(DELAY_OFF); // wait for DELAY_OFF msec

}

Analog to Digital Conversion

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ATMEGA328 ADC Features

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ADC Timing Diagram

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How to use ADC in Arduino?

Use the analogRead() function to read an analog value from a given pin:

void loop() {

int sensorValue = analogRead(A0); // Note: A0 is predefined

.....

}

A0-A5 can be used for analogRead()

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Pulse-width modulation (PWM)

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Pulse-width modulation (PWM) is a modulation technique used

in communications systems to encode the amplitude of a signal

into the width of the pulse (duration) of another signal.

its main use is to allow the control of the power supplied to

electrical devices, especially to inertial loads such as motors.

The term duty cycle describes the proportion of 'on' time to the

regular interval or 'period' of time

The main advantage of PWM is that power loss in the switching

devices is very low. When a switch is off there is practically no

current, and when it is on and power is being transferred to the

load, there is almost no voltage drop across the switch

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PWM in Arduino

analogWrite() writes an analog value (PWM wave) to a pin.

A call to analogWrite() is on a scale of 0 - 255, such that

analogWrite(255) requests a 100% duty cycle (always on), and

analogWrite(127) is a 50% duty cycle (on half the time) for

example.

The frequency of the PWM signal on most pins is approximately

490 Hz. On the Uno and similar boards, pins 5 and 6 have a

frequency of approximately 980 Hz.

On most Arduino boards, this function works on pins 3, 5, 6, 9,

10, and 11.

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avr programming

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