ATmega162 datasheet(185/324 Pages) ATMEL

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185

2513K–AVR–07/09

ATmega162/V

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

(e.g., by disabling interrupts globally) during the read operation.

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

Note:

1. The example code assumes that the part specific header file is included.

The assembly code example returns the UCSRC value in r16.

Reading the UBRRH contents is not an atomic operation and therefore it can be read as an ordi-

nary register, as long as the previous instruction did not access the register location.

Assembly Code Example(1)

USART_ReadUCSRC:

; Read UCSRC

r16,UBRRH

r16,UCSRC

ret

C Code Example

(1)

unsigned char

USART_ReadUCSRC( void )

{

unsigned char

ucsrc?

/* Read UCSRC ?/

ucsrc = UBRRH;

ucsrc = UCSRC;

return ucsrc;

}

ATmega162 Datasheet(PDF) 185 Page - ATMEL Corporation