Rainbow Electronics ATmega3290P_V - Manual (Page 169)

169
ATmega329/3290/649/6490
2552H–AVR–11/06
Sending Frames with 9 Data
Bit If 9-bit characters are used (UCSZ = 7), the ninth bit must be written to the TXB8n bit in
UCSRnB before the low byte of the character is written to UDRn. 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: 1. These transmit functions are written to be general functions. They can be optimized if
the contents of the UCSRnB is static. For example, only the TXB80 bit of the UCS-
RnB Register is used after initialization.
2. See “About Code Examples” on page 8.
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 (1)(2)
USART_Transmit:
; Wait for empty transmit buffer
sbis UCSR0A,UDRE0
rjmp USART_Transmit
; Copy 9th bit from r17 to TXB80
cbi UCSR0B,TXB80
sbrc r17,0
sbi UCSR0B,TXB80
; Put LSB data (r16) into buffer, sends the data
out UDR0,r16
ret
C Code Example (1)(2)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSR0A & (1<
;
/* Copy 9th bit to TXB80 */
UCSR0B &= ~(1<
if ( data & 0x0100 )
UCSR0B |= (1<
/* Put data into buffer, sends the data */
UDR0 = data;
}