Hiii………friend this is next tutorial on AVR microcontroller,
I know it took some time because I was trying to make it crystal clear for you
all. In this tutorial we are going to discuss about basic GPIO( general purpose
intput output) in AVRs.
All the interfacing of input and outputs of an AVR MCU is
performed through PORTs. Before starting anything take a look of ATMEGA 16.
Here you can see there are 32 I/O pins grouped as A,B,C,D
with 8 pins in a group. These groups are known as PORTs. You can see there are some
special functions written in bracket in
front of these I/O pins, these are are the special function which our AVR MCU
can perform with these specific pins other than I/O. we will discuss about all
these functions in upcoming tutorials.
REGISTERS
All the processes in a MCU are performed through the help of
registers. Register is a 8 bit location in the RAM. Here there are total 32x8
bit registers in ATMEGA16. Though the size of register is 8 bit that’s why it
is called an 8 bit MCU.
HOW TO CONFIGURE
INPUT /OUTPUT PROCESS IN MCU
Each PORT contain three type of registers.
DDRX- set weather
a PORT is input or output.
PORTX- setting
the value of output PORT.
PINX- reading the
value of input PORT
DDRX( Data Direction
Register)
With the help of this register we can make a port input PORT
or output PORT.
To make a pin input or output we set its corresponding bit
as
Set bit 1 to make it a output pin
Set bit 0 to make it a input pin.
So if we want to make all the pins of
PORT A as input pins and all the pins of PORT B as output pins ,in our code we
will write
DDRA=0x00; 0x for hexadecimal
DDRB=0x FF;
OR
DDRA=0b00000000; 0b for binary
DDRB=0b11111111;
Similarily if we want to make only first four pins of PORT C
as input and last four as output, we will write.
DDRC=0XF0;
OR
DDRC=0b11110000;
PORTX (PORTX DATA
REGISTER)
This register is used to set the value of a PORT, now a pin
can be input or output let see both the cases
OUTPUT PIN
A pin be set to HIGH OUTPUT +5V by setting it to 1, and can be set to LOW
OUTPUT OV by setting it to 0.
For example we want high output on PC0,PC1 pins of PORTC and
low output on rest of the pins of PORT C, then we can configure it as
PORTC=0x02;
OR
PORTC=0b00000011;
No the desired output sequence ia available on PORTC.
PINX ( Data read register)
This register is used to read the value of a PORT, If a pin
is set as input then corresponding pin can be read as
0 for low input
1 for high output.
Now suppose PORT C is input port and
we have connected a switch or sensor at PC0, then we can read the value of PC0
with the help of PINX register. You can read the state of key/switch by simply
reading the PINC. It will be ‘1’ when pressed and ‘0’ if un pressed.
CODING
...
if(PINC & 0b00000001)
{
//Switch is pressed
...
}
else
{
//Switch is not pressed
...
}
...
NOTE- all the input output functions needs the header file
<avr/io.h> it must be added at the starting of the program.
In case you are not getting this code , I will suggest you to go
through basics of C first. Download some tutorials from web or simply get any
book on basics of c/c++.
Now its time to use
all this stuff in a code so we are going to implement a simple input output
project in which a led will not glow as
output when switch will be pressed as input.
Here we are connecting the LED at PB0 and a push button at
PC0. When we push the switch LED does not glow otherwise it glows.
The source code is given below just compile this code get
hex file and program your MCU with this hex file.
/*
* IO_PROJECT.c
*
* Created: 10/16/2012
3:07:51 AM
* Author: ABHILASH
*/
#include<avr/io.h>
#include<util/delay.h>
int main(void)
{
DDRB=0xFF; // define PORT B as output PORT
DDRC=0x00; // define PORT C as input port
int s1=0;
// initializing and defining s1=0, acquire switch as s1
while(1) // create infinite loop
{
s1=PINC&0b00000001; // acquire switch status connected at PC0
if(s1==0b00000001) // check if switch is pressed
{
PORTB=0b00000000; // turn of led by setting PB0 at low output
}
else
{
PORTB=0b00000001; // turn on LED by setting PB0 as high output
}
}
}
Now implement this circuit on the breadboard and you will we
able to see the desired results…
Result will be like this.
.Switch pressed LED
not glowing.
Switch not pressed LED glowing
some times there occurs the problem of switch debouncing, we will discuss about that in any upcoming tutorial.
I hope this article was beneficial for beginners. in next tutorial we
will discuss about some other basics of AVR. If you have any
doubt, question or critical comment please post here.
THNX...:)
