Taking Input AVR
Taking Input AVR (Input Event Handelling)
#include<avr/io.h>
#include<util/delay.h>
int main(void)
{
DDRD=0xFE; // PORTD_0 declared as input
DDRA=0xFF; //PORTA is declared as output
PORTA=0×00; // initially LED off
PORTD=0xFF; // Internal pullup is enabled
while(1==1) // infinite loop
{
if(!(PIND & 0×01)) // check whether the switch is pressed or not
{
while(!(PIND & 0×01)); //wait for debounce
PORTA=(1<<3); // LED on
_delay_ms(500); // On for a half second
PORTA=0×00; // LED turns off
} // if ends here
} // while(1 ) ends here
return 0;
} // main ends here
Explanation- As we know that DDRx registers are used to set data direction of PORTx either as input or output. Since in this case switch is connected to PIN0 of PORTD, it is declared as input pin.
In case of taking input at any of the pins of controller it is very neccessary to externally or internally pullup the pin. Pull up is basically a resistance of about 10K which is used to pull the input pin in high state when the switch is not pressed. AVR family controllers has internal pullups which can be enabled by declaring the pin as input and writing a 1 initially to that pin (In our case it is PIN 0 of PORTD).
Debounce- when we press a mechanical switch, we think that it goes pressed for only once, but when we look the phenomenon in a microscopic way, it get pushed many times, which results in a undetermined state at last and this shown an abnormal behaviour when interfaced with the MCU. So to get rid off this problem concept of debounce is used.
According to debouncing concept the event occured when the switch is released and not when switch is pressed.
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Contact-
Devesh Samaiya
devesh@electroons.com
Ph- +91-9977411065
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