====== Input/Output am Study Board ======
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Study Board ‚Basic’ verfügt über drei Outputs (LEDs, verbunden mit PORT-C[3..5]) und drei Inputs (Mikroschalter an PORT-C[0..2]).

Dieses Beispiel zeigt wie die LEDs beim Drücken des entsprechenden Schalters aktiviert werden.


==== Schaltplan: ====

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==== Beispiel C Code: ====

<code c>
/* Labor 1 example

Description: Example works with Studyboard Basic v3
Press S1 - LED1 goes ON; S2 - LED2 goes ON; S3 - LED3 goes ON
LED = 0 (ON)  	LED = 1 (OFF)
S= 0 (ON) 	S= 1 (OFF)
PORT direction: 1-output	0-input 

Author: Raivo Sell 2008
*/

#include <avr/io.h>

#define F_CPU 14745600UL
//Definitions for easier bit manipulations
#define SET(x) |= (1<<x)  //bit high in port x
#define CLR(x) &=~(1<<x)  //bit low in port x

int main(void) { //main program

    DDRC  = 0x38;  // DDRC  0bXX111000
    PORTC = 0x3F;  // PORTC 0bXX111111

	//endless loop
	while(1) {
		// if button is pressed (pin is low)
		if (bit_is_clear(PINC, 0))	//Switch S1
			PORTC CLR(3); //LED 1 ON
		else if (bit_is_clear(PINC, 1))//Switch S2
			PORTC CLR(4); //LED 2 ON
		else if (bit_is_clear(PINC, 2))//Switch S3
			PORTC CLR(5); //LED 3 ON
		else // If nothing is pressed
			PORTC=0xFF;		//All LEDs OFF (LED=1)
	}
}
</code>

==== Beispiel (Kurzversion) ====


<code c>
/* Lab 1 example
Author: Maido Hiiemaa
Date: 2009
*/

#include <avr/io.h>

int main(void) {
     DDRC  = 0x38;  //  (00111000)
     while(1) {
        PORTC &= ~((PINC << 3) | 0xC7 ); // zeros
	PORTC |= ((PINC << 3) & ~0xC7 ); // ones
        }
}
</code>


==== Elliminating bouncing ====

Source: [[http://www.micahcarrick.com/05-15-2006/avr-tutorial-switch-debounce.html|Micah Carrick tutorial]]

<code c>
#include <avr/io.h>
#include <util/delay.h>

#define BUTTON_PORT PORTC       /* PORTx - nupu register */
#define BUTTON_PIN PINC         /* PINx - nupu sisendi register */
#define BUTTON_BIT PC0          /* nupu sisend/väljund bit */
 
int button_is_pressed()
{
        /* button is on when BIT is low (0) */
        if (bit_is_clear(BUTTON_PIN, BUTTON_BIT))
        {
                _delay_ms(25); /* de-bouncing delay time */
                if (bit_is_clear(BUTTON_PIN, BUTTON_BIT)) return 1;
        }
 
        return 0;
}
 
int main (void){
 
        /* switch on internel pull-ups */
        BUTTON_PORT |= _BV(BUTTON_BIT);
        if (button_is_pressed()){
                        //  do somthing
                        // wait if needed
        }
}
</code>