Write Access

When doing a write access of this I/O location, the high bit of the value written, the USART Register Select (URSEL) bit, controls which one of the two registers that will be written. If URSEL is zero during a write operation, the UBRRH value will be updated. If URSEL is one, the UCSRC setting will be updated.

The following code examples show how to access the two registers.

Assembly Code Example⁽¹⁾

:.
   ; Set UBRRH to 2
   ldi r16,0x02
   out UBRRH,r16
   :.
   ; Set the USBS and the UCSZ1 bit to one, and
   ; the remaining bits to zero.
   ldi r16,(1<<URSEL) | (1<<USBS) | (1<<UCSZ1)
   out UCSRC,r16
   :.

:.
   /* Set UBRRH to 2 */
   UBRRH = 0x02;
   :.
   /* Set the USBS and the UCSZ1 bit to one, and */
   /* the remaining bits to zero. */
   UCSRC = (1<<URSEL) | (1<<USBS) | (1<<UCSZ1);
   :.

Note: 1. See About Code Examples.

As the code examples illustrate, write accesses of the two registers are relatively unaffected of the sharing of I/O location.

Write Access

Assembly Code Example(1)

Assembly Code Example⁽¹⁾