ATMEGA169 ATMEL [ATMEL Corporation], ATMEGA169 Datasheet - Page 160

• Manufacturer Part Number: ATMEGA169
• Description: 8-bit Microcontroller with 16K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Sending Frames with 9 Data
Bit
160
ATmega169/V
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.
Notes:
The ninth bit can be used for indicating an address frame when using multi processor
communication mode or for other protocol handling as for example synchronization.
Assembly Code Example
C Code Example
USART_Transmit:
void USART_Transmit( unsigned int data )
{
}
; Wait for empty transmit buffer
sbis UCSRA,UDRE
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB8
cbi
sbrc r17,0
sbi
; Put LSB data (r16) into buffer, sends the data
sts
ret
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<<UDRE))) )
/* Copy 9th bit to TXB8 */
UCSRB &= ~(1<<TXB8);
if ( data & 0x0100 )
/* Put data into buffer, sends the data */
UDR = data;
1. These transmit functions are written to be general functions. They can be optimized if
2. See “About Code Examples” on page 6.
UCSRB |= (1<<TXB8);
the contents of the UCSRB is static. For example, only the TXB8 bit of the UCSRB
Register is used after initialization.
UCSRB,TXB8
UCSRB,TXB8
UDR,r16
;
(1)(2)
(1)(2)
2514P–AVR–07/06