Rainbow Electronics ATtiny2313 - Manual (Page 121)

121
ATtiny2313
2543A–AVR–08/03
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.
Notes: 1. These transmit functions are written to be general functions. They can be optimized if
the contents of the UCSRB is static. For example, only the TXB8 bit of the UCSRB
Register is used after initialization.
2. The example code assumes that the part specific header file is included.
For I/O Registers located in extended I/O map, “IN”, “OUT”, “SBIS”, “SBIC”, “CBI”,
and “SBI” instructions must be replaced with instructions that allow access to
extended I/O. Typically “LDS” and “STS” combined with “SBRS”, “SBRC”, “SBR”, and
“CBR”.
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 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)(2)
void USART_Transmit( unsigned int data )
{
/* Wait for empty transmit buffer */
while ( !( UCSRA & (1<
;
/* Copy 9th bit to TXB8 */
UCSRB &= ~(1<
if ( data & 0x0100 )
UCSRB |= (1<
/* Put data into buffer, sends the data */
UDR = data;
}