Datasheet

Assembly Code Example
(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Put data (r16) into buffer, sends the data
out UDR,r16
ret
C Code Example
(1)
void USART_Transmit( unsigned char data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE)) )
;
/* Put data into buffer, sends the data */
UDR = data;
}
Note: 1. See About Code Examples.
The function simply waits for the transmit buffer to be empty by checking the UDRE Flag,
before loading it with new data to be transmitted. If the Data Register Empty Interrupt is
utilized, the interrupt routine writes the data into the buffer.
Related Links
About Code Examples
24.6.2 Sending Frames with 9 Data Bits
If 9-bit characters are used (UCSZ = 7), the ninth bit must be written to the TXB8 bit in UCSRB before the
Low byte of the character is written to UDR. The following code examples show a transmit function that
handles 9-bit characters. For the assembly code, the data to be sent is assumed to be stored in registers
R17:R16.
Assembly Code Example
(1)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi UCSRB,TXB8
sbrc r17,0
sbi UCSRB,TXB8
; Put LSB data (r16) into buffer, sends the data
out UDR,r16
ret
C Code Example
(1)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE))) )
;
/* Copy 9th bit to TXB8 */
UCSRB &= ~(1<<TXB8);
if ( data & 0x0100 )
UCSRB |= (1<<TXB8);
/* Put data into buffer, sends the data */
UDR = data;
}
AVR 8-Bit Microcontroller
USART - Universal Synchronous and Asynchrono...
© 2017 Microchip Technology Inc.
Datasheet Complete
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