====== Suhtluskanal ======

Järgnevalt on toodud UART jadaliidese kasutamise näide. Programm võimaldab edastada tekstisõnumeid AVR ja teise AVR-i või arvuti vahel. Kasutatud on viikude, LCD ja USART teeke. 

<code c>
#include <stdio.h>
#include <avr/io.h>
#include <util/delay.h>
#include "pin.h"
#include "lcd.h"
#include "usart.h"

// Pin configuration
#define BUTTON_CHAR     PORTPIN(C, 0)
#define BUTTON_NEXT     PORTPIN(C, 1)
#define BUTTON_ENTER    PORTPIN(C, 2)

// Characters list
#define NUM_CHARS 26
const char chars[NUM_CHARS] = " ABCDEFGHIJKLMOPQRSTUVWXYZ";

// General configuration
#define MAX_MESSAGE     16

//
// My message variables
//
char my_message[MAX_MESSAGE + 3];	
unsigned char my_char_index = 0;
unsigned char my_char_position = 0;

//
// Incoming message variables
char rx_message[MAX_MESSAGE + 3];
unsigned char rx_char_position = 0;

//
// Resetting my message
//
void reset_my_message()
{	
	// Fill the message with nulls
	for (my_char_position = 0; my_char_position < MAX_MESSAGE + 3; my_char_position++)
	{
		my_message[my_char_position] = 0;
	}		

	// Reset indexes
	my_char_position = 0;
	my_char_index = 0;			
}

//
// Displaying my current message
//
void display_my_message()
{	
	lcd_gotoxy(0, 0);
	lcd_puts("                 ");
	lcd_gotoxy(0, 0);
	lcd_puts(my_message);
	lcd_gotoxy(my_char_position, 0);
}

//
// Resetting received message
//
void reset_rx_message()
{
	// Fill the message with nulls
	for (rx_char_position = 0; rx_char_position < MAX_MESSAGE + 3; rx_char_position++)
	{
		rx_message[rx_char_position] = 0;
	}

	// Reset position
	rx_char_position = 0;
}

//
// Displaying received message
//
void display_rx_message()
{	
	lcd_gotoxy(0, 1);
	lcd_puts("                 ");	
	lcd_gotoxy(0, 1);
	lcd_puts(rx_message);	
}

//
// Main function
//
int main(void)
{	
	// Button state variables	
	unsigned char button_char_new,  button_char_old  = 1;
	unsigned char button_next_new,  button_next_old  = 1;
	unsigned char button_enter_new, button_enter_old = 1;	

	// LCD configuring
	lcd_init(LCD_DISP_ON_BLINK);
	lcd_clrscr();

	// UART configuring
	usart0_init_async(USART_DATABITS_8, USART_STOPBITS_1, USART_PARITY_NONE, 9600);

	// Buttons configuring
	pin_setup_input(BUTTON_CHAR);
	pin_setup_input(BUTTON_NEXT);
	pin_setup_input(BUTTON_ENTER);

	// Reset
	reset_my_message();
	reset_rx_message();	

	// Endless cycle
	while (1)
	{
		// Get new button values
		pin_get_value(BUTTON_CHAR,  button_char_new);
		pin_get_value(BUTTON_NEXT,  button_next_new);
		pin_get_value(BUTTON_ENTER, button_enter_new);
			
		// Char selection button pressed ?
		if (!button_char_new && button_char_old)
		{
			// Change char
			my_char_index++;

			// Wrap
			if (my_char_index >= NUM_CHARS)
			{
				my_char_index = 0;
			}

			// Update message
			my_message[my_char_position] = chars[my_char_index];			

			// Display message text
			display_my_message();
			
			// Pause
			//_delay_ms(100);			
		}

		// Next char button pressed ?
		if (!button_next_new && button_next_old)
		{
			// Increase current position			
			my_char_position++;

			// If message is full, restart
			if (my_char_position >= MAX_MESSAGE)
			{
				reset_my_message();
			}
			else
			{
				// Fill new places with space
				my_char_index = 0;
				my_message[my_char_position] = chars[my_char_index];				
			}

			// Display message text
			display_my_message();

			// Pause
			//_delay_ms(100);
		}

		// Enter button pressed ?
		if (!button_enter_new && button_enter_old)
		{						
			// Send message if it's not empty
			if ((my_char_position > 0) || (my_message[0] != 0))
			{
				// Inser line feed and carriage return before terminator
				my_message[my_char_position + 1] = '\r';
				my_message[my_char_position + 2] = '\n';
				my_message[my_char_position + 3] = 0;
			
				// Send message
				usart0_send_text(my_message);

				// Restart
				reset_my_message();
				display_my_message();
			}
		}

		// Remember old button values
		button_char_old  = button_char_new;
		button_next_old  = button_next_new;
		button_enter_old = button_enter_new;
		
		// Got data ?
		if (usart0_has_data())
		{
			// Read char
			rx_message[rx_char_position++] = usart0_read_char();
			
			// Show message if it's too long or the delimiter has arrived
			if ((rx_char_position >= MAX_MESSAGE + 3) ||
				 ((rx_message[rx_char_position - 2] == '\r') && (rx_message[rx_char_position - 1] == '\n')))
			{
				// Replace line chars with null terminator
				rx_message[rx_char_position - 2] = 0;
				rx_message[rx_char_position - 1] = 0;

				// Display message
				display_rx_message();
				reset_rx_message();
			}
		}
	}
}
</code>