Datasheet

171
ATtiny828 [DATASHEET]
8371A–AVR–08/12
Note: 1. See “Code Examples” on page 7.
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.
17.6.2 Sending Frames with 9 Data Bit
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.
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;
}
Assembly Code Example
(1)(2)
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