How to interface AVR microcontroller with PC using USART (RS232 protocol)

       This article covers data transmission using 8 bit USART. The readers should have a basic understanding of serial communication and how to receive the serial data output. More  details on these topics  are available on Serial communication using AVR Microcontroller USART.

       The registers of USART system are already explained in previous article. Before transmitting the data, it must be stored in UDR register. The HyperTerminal software is used to show received data. The following steps can be followed to transmit the data to COM port of computer.
        i.            Monitor the status of UDRE (USART Data register Empty) flag.
       ii.            A high on the UDRE indicates that the UDR register is empty and ready to accept new data to be sent.
void usart_putch(unsigned char send)
{
    while ((UCSRA & (1 << UDRE)) == 0); // Do nothing until UDR is ready..
                                        // for more data to be written to it
    UDR = send; // Send the byte
}

// Program to receive data from USART and displaying that..
// data on LCD and sending the same data on HyperTerminal.
/*
get data from serial port and displaying it on LCD and send back to the HyperTerminal
LCD DATA port----PORT A
ctrl port------PORT B
    rs-------PB0
    rw-------PB1
    en-------PB2
@ external clock frequency 12MHz
*/

#define F_CPU 12000000UL

#define USART_BAUDRATE 9600
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)

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

#define LCD_DATA PORTA        // LCD data port
#define ctrl PORTB
#define en PB2        // enable signal
#define rw PB1        // read/write signal
#define rs PB0        // register select signal

void LCD_cmd(unsigned char cmd);
void init_LCD(void);
void LCD_write(unsigned char data);
void LCD_clear();

void usart_init();
void usart_putch(unsigned char send);
unsigned int usart_getch();

int main()
{
    unsigned char value;
    DDRA=0xff;       
    DDRB=0x07;       
    init_LCD();        //initialization of LCD
    _delay_ms(50);        // delay of 50 mili seconds
    usart_init();        // initialization of USART
    while(1)
    {
        value=usart_getch();    // get data from serial port
        LCD_cmd(0xC0);           
        LCD_write(value);        // write data to LCD
        usart_putch(value);        // send data back to the PC (HyperTerminal)
    }
    return 0;
}

void init_LCD(void)
{
    LCD_cmd(0x38);        //initialization of 16X2 LCD in 8bit mode
    _delay_ms(1);

    LCD_cmd(0x01);        // clear LCD
    _delay_ms(1);

    LCD_cmd(0x0E);        // cursor ON
    _delay_ms(1);

    LCD_cmd(0x80);        // ---8 go to first line and --0 is for 0th position
    _delay_ms(1);
    return;
}

void LCD_cmd(unsigned char cmd)
{
    LCD_DATA=cmd;
    ctrl =(0<<rs)|(0<<rw)|(1<<en);   
    _delay_ms(1);
    ctrl =(0<<rs)|(0<<rw)|(0<<en);   
    _delay_ms(50);
    return;
}

void LCD_write(unsigned char data)
{
    LCD_DATA= data;
    ctrl = (1<<rs)|(0<<rw)|(1<<en);   
    _delay_ms(1);
    ctrl = (1<<rs)|(0<<rw)|(0<<en);   
    _delay_ms(50);   
    return ;
}

void usart_init()
{
    UCSRB |= (1 << RXEN) | (1 << TXEN);  
                    // Turn on the transmission and reception circuitry
    UCSRC |= (1 << URSEL) | (1<<USBS) | (1 << UCSZ0) | (1 << UCSZ1);
                    // Use 8-bit character sizes

    UBRRL = BAUD_PRESCALE; // Load lower 8-bits of the baud rate value..
                            // into the low byte of the UBRR register
    UBRRH = (BAUD_PRESCALE >> 8); // Load upper 8-bits of the baud rate value..
                                    // into the high byte of the UBRR register
}

void usart_putch(unsigned char send)
{
    while ((UCSRA & (1 << UDRE)) == 0); // Do nothing until UDR is ready..
                            // for more data to be written to it
    UDR = send; // Send the byte
}

unsigned int usart_getch()
{
    while ((UCSRA & (1 << RXC)) == 0);
                // Do nothing until data have been received and is ready to be read from UDR
    return(UDR); // return the byte
}

  

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