How to interface AVR microcontroller with PC using USART (RS232 protocol)- (Part 13/46)

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

}

Project Source 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
}
 
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