Topic: Introduction to Atmega 8 and its basic architectures to start with!!!
Refer to this data sheet, while I describe it to you.
Okay, Here you can see some of the properties of Atmega8 Ic that you need to know for now:
1. Operating Voltages: (2.7v to 5.5v) for atmega8L (Low power atmega) and (4.5v to 5.5v) for Atmega8.
** This should be very clear from the first, these digital ICs work like logical 0 for 0 v to 2.5v and logical 1 for 2.5v to 5.5v and above 5.5 the MCU won't recognize the i/p voltage.
2. (0-8)mhz Crystal for Atmega8L and (0-16)mhz Crystal for Atmega8.
** Crystal is the clock frequency needed for the MCU for its processing. These are basically the heart-beat of the system. Clock Frequency is analogous to the processor speed of our PCs.
3. There are 32 Register Blocks of 8 bit each (as Atmega is 8bit mcu).
4. 6 channel, 10 bit ADC and 3 channel PWM are available.
I/O Registers of Atmega8
There are 3 Ports in Atmega 8 viz Port B, Port C and Port D.
Each of the pins of the ports can be used as General Purpose Input/Output Pins.
They are used for sensing an input device like switches, temperature/humidity sensor, IR etc or running an output device like Leds, Motors etc.
N.B: A particular pin can be used as either input or output at a time.
To work with the I/O pins, three registers of 8 bits each have to be configured viz., DDRX, PORTX and PINX. (here 'X' indicates the name of the register B,C or D)
Data Direction Register (DDRX) :
A MCU doesnot know what type of device is interfaced to its pins unless the programmer mentions it inside the code. Thus, we have to set its corresponding DDR bits as 0 or 1 in our code. Thus DDRX code is used to inform the MCU that it should give voltage to a certain pin or check the status of the pin.
For Eg. : Let there is a Led (output device) connected to PB0, So the first bit of the PORTB register should be 1 and the rest are 0s.
Note:
- If a pin has nothing on it or it has an input device, that pin should be given 0 any way.
- The register bits are arranged from MSB to LSB as follows.
PORTX Register :
This register is used to give a logical 1 or 0 output at the output pins. Logical 1 represents voltages between 2.5 and 5.5. logical 0 repesents voltages between 0 and 2.5.
PINX Register :
This register is used to check the status of an input pin. It reads the analog or digital data from switches and sensors.
Sample Code:
1. Blinking Leds code.
#include<avr/io.h> // Header File for AVR MCU.
#include <util/delay.h> // Header File for delay functioning.
int main(void)
{
DDRB=0b00001111; // PB0 to PB3 are selected as the output pins, i.e., leds are connected to pins 14,15,16,17 of atmega8.
while(1) //This is for the the infinity loop.
{
PORTB=0b00001111; //Switch on all 4 LEDs
_delay_ms(2000); //Delay of 2sec=2000 ms
PORTB=0b00000000; //Switch off all 4 LEDs
_delay_ms(2000); //Delay of 2sec=1000 ms
}
}
Circuit Diagram:
