2.8.1 Common Functionality

The basic operation of USART is similar for both families, but the register and bit names are different. The AVR Dx devices have an improved register structure that allows a more efficient access to the configuration/status bits.

The following section details the mapping of ATmega128 registers into AVR Dx register structure (only ATmega registers and AVR Dx correspondences are figured):

The following code snippets shows the initialization of the USART peripheral for both families:

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

void USART_Init(void){
   /* Set baud rate */
   UBRRL = BAUD_PRESCALE;             /* Load lower 8 bits into the low byte of the UBRR register */
   UBRRH = (BAUD_PRESCALE >> 8);      /* Load upper 8 bits into the high byte of the UBRR register */

   UCSRB = (1<<RXEN)|(1<<TXEN);       /* Enable receiver and transmitter */
   UCSRC = (1<<USBS)|(3<<UCSZ0);      /* Set frame format: 8data, 1 stop bit */
}

#define USART1_BAUD_RATE(BAUD_RATE)     ((float)(64 * 4000000 / (16 * (float)BAUD_RATE)) + 0.5)

void USART1_init(void)
{
    USART1.BAUD = (uint16_t)(USART1_BAUD_RATE(9600));   /* set the baud rate*/
    
    USART1.CTRLC = USART_CHSIZE0_bm
                 | USART_CHSIZE1_bm; /* set the data format to 8-bit*/
                 
    USART1.CTRLB |= USART_RXEN_bm | USART_TXEN_bm;      /* enable receiver and transmitter*/
}