AVR-BOTskol Tutorial

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Input Output Operations using AVR

StudioSubmitted by bOtskOOl on Sun, 06/21/2009 - 04:25

This is the very first tutorial of the AVR (Atmega-16/32) tutorial series. Note that in thisand subsequent tutorials most of the examples will be based on Atmega32, though they

can be implemented on Atmega16 too without any major changes. If and when some

changes are required to be made it will be mentioned. So lets begin, first of all we willbe discussing AVR studio which is an editor, assembler, compiler, simulator and much

more. In this tutorial we will discuss the coding part in assembly language. Many people

run away from assembly language programming but when you start learning

microcontrollers properly and thoroughly and write your own programs the assemblygives much easier ability to think, anaylse and apply the logic to make your programs and

you can directly take advantage of microcontrollers architecture while writing your

program. If you want you can shift to C very easily after that, it is just a step away afteryou have learnt assembly. We shall be launching AVR C tutorial series in a few days.

Atmega-16/32 Pin Description


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Physical Ports of Atmega-16/32

The Atmega-16/32 has four physical ports on the chip as marked in the figure above.These ports are named as PortA, PortB, PortC and PortD. Each port is basically a

collection of 8 pins grouped together.


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Basic Circuit of AVR

The pins marked Gnd are to be grounded, Vcc & AVcc are to be given 5V. The resetpin is also high but we usually prefer to put a switch at this point for the reset of the

chips. If the switch is pressed for a minimum pulse of time then it will reset the chip.

Note: AVcc should be connected to 5V supply through a capacitor when using PORTA

pins as ADC, though in simple applications capacitor is not necessary.

This circuit is used whenever we wish to do anything with the controller. In addition tothis you will have to add other hardware required depending upon what do you want to

accomplish.


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Now for the given tutorial we will be using the PORTB for connections. We will connect

8Leds at each pin of PORTB.

The above picture depicts how each LED will be connected to corresponding pin of

portB of Atmega32. So lets see the complete circuit


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Complete Circuit Diagram

Photograph of switch

The switch is required so that we are able to reset i.e. restart the microcontroller at any

time if required.

People who have worked on some other microcontroller must be familiar with word

Registers.

In short, registers are used to store information temporarily. That information can be of

one byte (or two) of data to be processed or an address pointing to data to be fetched.

The AVR has 32 general purpose registers and many other registers also. There are threeregisters associated with each port that are required for the Input-Output operation for

AVR. These registers are DDRx register, PORTx register, PINx register where x can be

(A, B, C, D). These register are very important and are used for reading and writing to theports.

Note: The physical ports and the register PORTx has same name but the user must notconfuse between them, from now on while discussing register PORTx it will be referred

as PORTx Register to avoid confusion.

These registers will be discussed later on in detail but before that lets write our first

program and try to understand it.


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Download the AVR Studio from Atmel and install it. We will be showing you how to

start working directly with the software. It is an environment where can write your

programs, build corresponding hex codes, do debugging and much more!

You will be also needing the datasheet ofAtmega16orAtmega32.

Using the datasheet

If you are beginner do not go through the datasheet now as you will find it quite difficult

to understand. Luckily you are not supposed to do that, either. The datasheets are

complete technical documents that you should use as a reference when you are in doubthow a given peripheral or feature works.

We will be covering the necessary theories and relevant concepts as we move on and in

no time you will have confidence to write your own programs.

After you have downloded and installed AVR Studio, just open the it and follow thesteps

STARTING A NEW PROJECT IN AVR STUDIO

STEP-1

When you will launch the AVR Studio a splash screen will appear as shown below. In

case it doesnt choose New Project option from the Project menu.
http://www.atmel.com/dyn/products/tools_card.asp?tool_id=2725http://www.atmel.com/dyn/resources/prod_documents/doc2466.pdfhttp://www.atmel.com/dyn/resources/prod_documents/doc2466.pdfhttp://www.atmel.com/dyn/resources/prod_documents/doc2503.pdfhttp://www.atmel.com/dyn/resources/prod_documents/doc2503.pdfhttp://www.atmel.com/dyn/products/tools_card.asp?tool_id=2725http://www.atmel.com/dyn/resources/prod_documents/doc2466.pdfhttp://www.atmel.com/dyn/resources/prod_documents/doc2503.pdf


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STEP-2

Choose New Project as shown above.

STEP-3

Choose Atmel AVR Assembler option in Project type:

Write the Project name (It doesnt accept a space in name). Choose a suitable Location & hit NEXT>>.


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STEP-4

Choose the debug platform in this case AVR Simulator.

Choose the device (Here we have chosen Atmega32 for our project) & click on

FINISH.

Now we can start our first project and understand the basics of I/O (Input/Output)

operations.

We will learn how the value of the I/O registers changes. AVR Studio has a fantastic tool

for showing step by step execution. Lets get started!


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As shown in the figure above

Region 1 Write your program here

Region 2 Menu bars (obviously you know this )

Region 3 You know what it is yes toolbar section

Region 4 I/O View

Region 5 Project directory and distribution

Region 6 Name of the microcontroller which is currently in use

When you will write your code you will notice that the instructions, comments, etc will

be written in different colors. This is a very important feature of an editor. Thisremarkably helps in distinguishing between types of syntaxes and lines.


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Below is a screenshot of our very first AVR code.

Lets understand the program before going further:


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Status of pin when configured as an output pin:-

PORTxn= 0, the output is driven high.

PORTxn= 1, the portx nth pin is driven low (zero).

PINx Register:-

To put it bluntly, the PINx register contains the status of all the pins in that port.

If the pin is an input pin, then its corresponding bit will mimic the logic level

given to it.

If it is an output pin, its bit will contain the data that has been previously outputon that pin. (The value of an output pin is latched to PINxn bit, you can observe it

when we do step by step execution in AVR-Studio shown below)

Click on Build and Run option present in Build menu bar.

We can observe the values of registers, Program counter, Cycle Counter, Port registers

and much more after execution of each instruction!

We can do step by step execution in AVR Studio by pressing F11 after code has been

successfully built and is running Lets do it.


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Region 5 - This confirms that are program has been successfully completed,Congratulation!!

Region 1 - This mark indicates the instruction to be executed in RAM.

Region 2 - This indicates location of Flash memory (ROM), the program are

burned in EEPROM and executed in RAM. (The beginners may find this concept

little confusing but dont worry for now just move on, we shall discuss it somelater on).

Region 3 - You can look at the current values of register by pressing the (+).

Region 4 - You can also get the values of the register associated with the

PORTB.

Now press F11 once, the arrow jumps to the next position as shown..


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Note the value of R16 by scrolling down, you will find it zero.

Clock Cycle is shown in blue colour on left hand side. This indicates the number

of clock cycles after the program started executing. An instruction can take one ortwo clock cycles.

On Pressing F11 again you will observe this

And Pressing F11 again...


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The PORTB is set as an output (the register DDRB is set)

Pressing F11 again we can see that


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The PORTB register is loaded with 255, this output to the pins of PORTB (1111

1111b) and all the LEDs start glowing

If we Press F11 again we will observe this


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The PINx register is latched with the value which was the output before this. This

proves the fact that the output values from pins are latched to register bits PINxnafter one cycles

Keep on playing with this by pressing F11 again and again & observe things till you

understand everything properly and are completely satisfied.

Burning the ROM of microcontroller

To get the hex file (that you will need to burn to your microcontroller) just open the

folder where you have saved your project.

In this case it is - D:\testprog\1


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You can buy a board to burn the AVR or build your own ISP, this topic will be covered

in next tutorial and by that time you can check out this tutorial - Parallel Port Programmerfor ATMEGA 16/32 - by one of our users - heloitsadi.
http://www.botskool.com/user-pages/tutorials/electronics/parallel-port-programmer-atmega-1632http://www.botskool.com/user-pages/tutorials/electronics/parallel-port-programmer-atmega-1632http://www.botskool.com/user-pages/tutorials/electronics/parallel-port-programmer-atmega-1632http://www.botskool.com/user-pages/tutorials/electronics/parallel-port-programmer-atmega-1632


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Parallel Port Programmer for ATMEGA

16/32

Submitted by heloitsadi on Sun, 06/07/2009 - 07:18

In-system programmer means we can design a programmer circuit using simple parallelport interfacing such that our controller can be directly burned with the program while in

the designed system or circuit board.

Following pins of Atmega16 are used in programmer circuit-

SCK Port B, Pin 7

SCK: Master Clock output, Slave Clock input pin for SPI channel. When the SPI isenabled as a Slave, this pin is configured as an input regardless of the setting of

DDB7.When the SPI is enabled as a Master; the data direction of this pin is controlled by

DDB7. When the pin is forced by the SPI to be an input, the pull-up can still becontrolled by the PORTB7 bit.

MISO Port B, Pin 6

MISO: Master Data input, Slave Data output pin for SPI channel. When the SPI is

enabled as a Master, this pin is configured as an input regardless of the setting of DDB6.When the SPI is enabled as a Slave, the data direction of this pin is controlled by DDB6.When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the

PORTB6 bit.

MOSI Port B, Pin 5


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MOSI: SPI Master Data output, Slave Data input for SPI channel. When the SPI is

enabled as a Slave, this pin is configured as an input regardless of the setting of DDB5.

When the SPI is enabled as a Master, the data direction of this pin is controlled by DDB5.When the pin is forced by the SPI to be an input, the pull-up can still be controlled by the

PORTB5 bit.

RESET-Pin 9

Reset Input. A low level on this pin for longer than the minimum pulse length willgenerate a reset, even if the clock is not running.

VCC -Pin 10

Digital supply voltage(+5V).

GND-Pin-11

Ground.

Parallel Port-

Parallel Port interfacing is the simplest method of interfacing. Parallel Ports are

standardized under the IEEE 1284 standard first released in 1994. It has data transferspeed up to 1Mbytes/sec. Parallel port is basically the 25 pin Female connector (DB-25)

in the back side of the computer (Printer Port). It has 17 input lines for input port and 12

pins for output port. Out of the 25 pins most pins are Ground and there is data register (8bit), control register (4 bit) and status register (5 bit).


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Figure-Pin diagram of Parallel Port

Following Pins are used in parallel port-

Interfacing -

In programmer circuit pins of parallel port which are above described has to interface

with pins of ATmega16 microcontroller which are responsible for in-systemprogramming. The parallel port can be interfaced directly with microcontroller. To avoid

reverse current we can use Schottkey diodes as safety precaution for pc motherboard.

Following pins of Parallel Port and ATmega16 are to be interfaced-


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Figure-Circuit Diagram of ATmega16 Programmer

SOFTWARES USED:

WinAVR WinAVR is open source package in which we use two sub-programs.

o Programmers Notepad

o Mfile.

Version- 2.0.8.718-basic

Creator- Simon Steele

Purpose-


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o To write code.

o To compile coding.

o To generate Hex Code.

o To burn Hex code.

The next tutorial will make you aware with how to install and use WinAVR forcompiling and burning the program.

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