ATMEGA8_08 Datasheet, PDF (152/308 Pages) ATMEL Corporation – 8-bit with 8K Bytes In-System Programmable Flash

Accessing
UBRRH/UCSRC
Registers
Write Access
The UBRRH Register shares the same I/O location as the UCSRC Register. Therefore some
special consideration must be taken when accessing this I/O location.
When doing a write access of this I/O location, the high bit of the value written, the USART Reg-
ister 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 Examples⁽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
...
C Code Examples⁽¹⁾
...
/* 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” on page 8.
As the code examples illustrate, write accesses of the two registers are relatively unaffected of
the sharing of I/O location.
152 ATmega8(L)
2486T–AVR–05/08