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Atmega8 Uc: Timer0 !!!

There are three timers in the Atmega8 microcontroller: Timer 0, Timer 1, and Timer 2. Timer 0 and Timer 2 are 8-bit timers, while Timer 1 is 16-bit. The timers use registers like TCNTx, TCCRx, TIMSK, and TIFR to control their operation and store data. The TCNTx register increments automatically at a fixed rate determined by the prescaler setting in TCCRx. When TCNTx overflows, an interrupt flag is set in TIFR. An example program uses Timer 0 in overflow mode with a prescaler of 64 to generate an interrupt every 61 counts, creating a 1 second delay.

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406 views17 pages

Atmega8 Uc: Timer0 !!!

There are three timers in the Atmega8 microcontroller: Timer 0, Timer 1, and Timer 2. Timer 0 and Timer 2 are 8-bit timers, while Timer 1 is 16-bit. The timers use registers like TCNTx, TCCRx, TIMSK, and TIFR to control their operation and store data. The TCNTx register increments automatically at a fixed rate determined by the prescaler setting in TCCRx. When TCNTx overflows, an interrupt flag is set in TIFR. An example program uses Timer 0 in overflow mode with a prescaler of 64 to generate an interrupt every 61 counts, creating a 1 second delay.

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malhiavtarsingh
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© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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ATMega8 uC

Timer0 !!!

WHAT ARE TIMERS?


Timer counts the time sequence or the clock pulses of the microcontroller

They are set of registers microcontroller

integrated in

most of the

Number of Timers in Atmega8

There are three timers/Counters in

Atmega8

Timer 0

Timer 1

Timer 2

Number of Timers in Atmega8


There are three timers/Counters in Atmega8

Timer 0

Timer 1

Timer 2

8-bit

16-bit

8-bit

Registers of Timers/Counters
There are four registers to control the operation & data storage TCNTx= Timer Counter Register TCCRx= Timer/Counter Control Register TIMSK= Timer Interrupt Mask Register TIFR= Timer Interrupt Flag Register

TIMER/COUNTER 0 REGISTER

TCNTx

This magical 8 bit register increases its own value with a fix rate. This register dont require CPU to increase its value. TCNTx keeps the count value from 0-255, it must be initialized in program code. When the count value reaches maximum, it raises a interrupt bit in another register and reset to 0 on overflow

Timer Frequency and Prescaling


Timer frequency is the rate by which TCNTx register increases its own value A prescalar measures an output clock/ time related to an input clock/time by a fractional scale factor

CS0, CS1. CS2: Prescalar select inputs.

TIMER/COUNTER CONTROL REGISTER

The timer control register controls Timer Frequency, this is achieved by setting the prescalar value

CS00-CS02 are used to select PRESCALER value and hence determines the frequency of the timer

PRESCALAR

TIMER FREQUENCY =CPU CLOCK FREQUENCY PRESCALER

TIMER INTERRUPT MASK REGISTER

Bit 0 or TOIE0 bit of TIMSK is used to enable/disable overflow interrupt of TIMER0 Storing 1 at this place will Enable the overflow interrupt of TIMER0 Storing 0 at this place will Disable the overflow interrupt of TIMER0 Other bits are used for other timers

OVERFLOW MODE
Once the timer reaches it highest counts and if it not resets it is said to be in Overflow Mode

For this mode we have to set 3 registers TCNT0 (To initialize counter) TCCR0 (To set Prescalar) TIMSK (To enable overflow interrupt)

Program for creating 1 sec delay using OVERFLOW mode


#include<avr/io.h> #include<avr/interrupt.h> volatile uint8_t count; main() { int second=0; char buffer[10]; TCCR0=0b00000011; //to set the prescalar to64 TIMSK |=(1<<TOIE0); //for enabling overflow interrupt TCNT0=0; //for initialization of Timer count

Contd
count=0; sei(); //Enable Global Interrupt while(1); } //main close ISR(TIMER0_OVF_vect) // interrupt service routine { if(count==61) // if count reaches 1 sec { second++; sprintf(seconds:%d, second); lcd_puts(buffer); // for printing seconds on LCD count=0; // reset the count variable } else count++; } //ISR function close

Description of program
if(count==61) // if count reaches 1 sec 61 is decided by clock frequency and the prescalar. Formula for calculating number of interrupts for 1 second time duration is : Timer frequency = CPU clock frequency/Prescalar No of overflow interrupts = Timer frequency/256 In our case: Timer frequency = 1000000/64 = 15625 No of interrupts = 15625/256 = 61.035 61

THANK YOU!!!

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