參數(shù)資料
型號: MQ80C52XXX-36/883
廠商: ATMEL CORP
元件分類: 微控制器/微處理器
英文描述: 8-BIT, MROM, 36 MHz, MICROCONTROLLER, CQFP44
封裝: CERAMIC, QFP-44
文件頁數(shù): 54/152頁
文件大?。?/td> 2528K
代理商: MQ80C52XXX-36/883
147
2486AA–AVR–02/2013
ATmega8(L)
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.
Note:
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
USART_ReadUCSRC:
; Read UCSRC
in
r16,UBRRH
in
r16,UCSRC
ret
C Code Example
unsigned char
USART_ReadUCSRC( void )
{
unsigned char
ucsrc;
/* Read UCSRC */
ucsrc = UBRRH;
ucsrc = UCSRC;
return ucsrc;
}
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