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

Developed By: 

Akshay Daga

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 

}

Circuit:

Code:

// 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

}