AVR ATmega32 Mini Development Board – Serial Communication (USART)

The USART module of ATmega32 uses pins PD0 & PD1 for reception & transmission respectively. The mini development board can communicate with PC/external modules through

USB port via CP2102
Serial port via MAX232
RMC connector K10 in 5V level
RMC connector K16 in 3.3V level

Besides, USART is also used for interfacing Zigbee & RFID reader.

Note :

USART communication via USB/serial port is selected using jumpers J1 & J2
Short jumpers J13 & J14 while using 3V3 USART / Zigbee
Remove jumpers J1 & J2 while using Zigbee / RFID/ UART (3V3/ 5V)

Schematic

Sample Code

The sample code to check USART module is given below. Initially the letter ‘A’ gets transmitted. Then, upon receiving a character, the same gets retransmitted.

Value in UBRR is calculated as follows
UBRR = (Fosc / (16 * BAUD)) – 1

The desired baudrate is 9600 bps and crystal frequency, Fosc is 8 MHz. This gives UBRR = 51. Any change in crystal frequency/baudrate changes this value as per the above equation.

/**************************************************************************************
                                     HEADER FILE
***************************************************************************************/
#include<avr/io.h>                  

/**************************************************************************************
                                 VARIABLE DECLARATION
***************************************************************************************/ 
volatile char Rec_Data;             

/**************************************************************************************
                                    MAIN FUNCTION
***************************************************************************************/      
int main()
{                  
 DDRD  = 0X02;                    /* PD0(RX)-I/P, PD1(TX)-O/P                         */
 UCSRA = 0X00;                    /* Clears TXC & RXC Flag Bit                        */
 UCSRB = 0X18;                    /* Transmission & Reception Enable (TXEN=1, RXEN=1) */														
 UCSRC = 0X86;                    /* URSEL=1,UMSEL=0,UCSZ1=1,UCSZ0=0                  */
 UBRRL = 51;                      /* Serial Baudrate=9600                             */
 UDR   = 'A';                     /* Transmit a charcter                              */				   
 while((UCSRA & 0X20)!=0X20);     /* UDRE Flag Bit Check                              */

 while(1)
 {
  while((UCSRA & 0X80)!=0X80);    /* RXC is set when unread data is in receive buffer */
  Rec_Data=UDR;                   /* Store the received character                     */
  UDR = Rec_Data;                 /* Transmit the received character                  */	   
  while((UCSRA & 0X20)!=0X20);    /* Wait here till UDR is empty                      */
 }
}

/**************************************************************************************
                                        END
***************************************************************************************/

/**************************************************************************************

HEADER FILE

***************************************************************************************/

#include<avr/io.h>

/**************************************************************************************

VARIABLE DECLARATION

***************************************************************************************/

volatile char Rec_Data;

/**************************************************************************************

MAIN FUNCTION

***************************************************************************************/

int main()

{

DDRD = 0X02; /* PD0(RX)-I/P, PD1(TX)-O/P */

UCSRA = 0X00; /* Clears TXC & RXC Flag Bit */

UCSRB = 0X18; /* Transmission & Reception Enable (TXEN=1, RXEN=1) */

UCSRC = 0X86; /* URSEL=1,UMSEL=0,UCSZ1=1,UCSZ0=0 */

UBRRL = 51; /* Serial Baudrate=9600 */

UDR = 'A'; /* Transmit a charcter */

while((UCSRA & 0X20)!=0X20); /* UDRE Flag Bit Check */

while(1)

{

while((UCSRA & 0X80)!=0X80); /* RXC is set when unread data is in receive buffer */

Rec_Data=UDR; /* Store the received character */

UDR = Rec_Data; /* Transmit the received character */

while((UCSRA & 0X20)!=0X20); /* Wait here till UDR is empty */

}

/**************************************************************************************

END

***************************************************************************************/

OutputThe following screenshots explain how to test the sample code using RealTerm (click to download).

Step 1: Open RealTerm

Step 2: RealTerm opens as shown below
Step 3: Go to ‘Port’ option, set correct baudrate (which is set as 9600 in the sample code) and correct port
Step 4: Click ‘Change’ (encircled in red) to apply the changes. Now check the status of Port. If it is closed, click ‘Open’ button (encircled in green) to open it.
Step 5: To check reception, go to Send option, type the string in the space provided(encircled in green) and click Send ASCII button. The first “hello” in green colour is transmitted from PC & that in yellow colour is retransmitted by the controller