ATmega16A datasheet(165/352 Pages) ATMEL

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165

8154B–AVR–07/09

ATmega16A

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

Note:

1. See “About Code Examples” on page 7.

As the code examples illustrate, write accesses of the two registers are relatively unaffected of

the sharing of I/O location.

19.10.2

Read Access

Doing a read access to the UBRRH or the UCSRC Register is a more complex operation. How-

ever, in most applications, it is rarely necessary to read any of these registers.

The read access is controlled by a timed sequence. Reading the I/O location once returns the

UBRRH Register contents. If the register location was read in previous system clock cycle, read-

ing the register in the current clock cycle will return the UCSRC contents. Note that the timed

sequence for reading the UCSRC is an atomic operation. Interrupts must therefore be controlled

(for example by disabling interrupts globally) during the read operation.

The following code example shows how to read the UCSRC Register contents.

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

C Code Example

(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);

Assembly Code Example

(1)

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