Write an AVR assembly code that waits for 1 sec using the 8-bit Timer/Counter0 w
ID: 3670376 • Letter: W
Question
Write an AVR assembly code that waits for 1 sec using the 8-bit Timer/Counter0 with the system clock frequency of 16 MHz operating under Normal mode. This is done by doing the following:
(1) Timer/Counter0 is initialized to count for 10 ms and then interrupts on an overflow;
(2) The main part of the program simply loops, and for each iteration, a check is made to see if the loop has reach 100 iterations; and
(3) On each interrupt, Timer/Counter0 is reloaded to interrupt again in 10 ms.
Use the skeleton code shown below:
.include “m128def.inc”
.def mpr = r16
.def counter = r17
…
.ORG $0000
RJMP Initialize
.ORG $0020 ; Timer/Counter0 overflow interrupt vector
RCALL Reload_Counter
RETI
.ORG $0046 ; End of interrupt vectors
Initialize:
…
…Your code goes here…
…
LOOP:
…
…Your code goes here…
…
…
Reload_counter:
…
…Your code goes here…
…
RET
Explanation / Answer
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#include <avr/io.h>
// initialize timer, interrupt and variable
void timer1_init()
{
// set up timer with prescaler = 64 and CTC mode
TCCR1B |= (1 << WGM12)|(1 << CS11)|(1 << CS10);
// initialize counter
TCNT1 = 0;
// initialize compare value
OCR1A = 24999;
}
int main(void)
{
// connect led to pin PC0
DDRC |= (1 << 0);
// initialize timer
timer1_init();
// loop forever
while(1)
{
// check whether the flag bit is set
// if set, it means that there has been a compare match
// and the timer has been cleared
// use this opportunity to toggle the led
if (TIFR & (1 << OCF1A)) // NOTE: '>=' used instead of '=='
{
PORTC ^= (1 << 0); // toggles the led
}
// wait! we are not done yet!
// clear the flag bit manually since there is no ISR to execute
// clear it by writing '1' to it (as per the datasheet)
TIFR |= (1 << OCF1A);
// yeah, now we are done!
}
}
So
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#include <avr/io.h>
// initialize timer, interrupt and variable
void timer1_init()
{
// set up timer with prescaler = 64 and CTC mode
TCCR1B |= (1 << WGM12)|(1 << CS11)|(1 << CS10);
// initialize counter
TCNT1 = 0;
// initialize compare value
OCR1A = 24999;
}
int main(void)
{
// connect led to pin PC0
DDRC |= (1 << 0);
// initialize timer
timer1_init();
// loop forever
while(1)
{
// check whether the flag bit is set
// if set, it means that there has been a compare match
// and the timer has been cleared
// use this opportunity to toggle the led
if (TIFR & (1 << OCF1A)) // NOTE: '>=' used instead of '=='
{
PORTC ^= (1 << 0); // toggles the led
}
// wait! we are not done yet!
// clear the flag bit manually since there is no ISR to execute
// clear it by writing '1' to it (as per the datasheet)
TIFR |= (1 << OCF1A);
// yeah, now we are done!
}
}
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