ATMEGA640 datasheet(217/449 Pages) ATMEL

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217

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

Sending Frames with 9 Data

Bit

If 9-bit characters are used (UCSZn = 7), the ninth bit must be written to the TXB8 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 TXB8 bit of the UCSRnB

2. See “About Code Examples” on page 9.

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

UCSRnA,UDREn

rjmp

USART_Transmit

; Copy 9th bit from r17 to TXB8

cbi

UCSRnB,TXB8

sbrc

r17,0

sbi

UCSRnB,TXB8

; Put LSB data (r16) into buffer, sends the data

out

UDRn,r16

ret

C Code Example

(1)(2)

void

USART_Transmit( unsigned int data )

{

/* Wait for empty transmit buffer */

while

( !( UCSRnA & (1<<UDREn))) )

;

/* Copy 9th bit to TXB8 */

UCSRnB &= ~(1<<TXB8);

if ( data & 0x0100 )

UCSRnB |= (1<<TXB8);

/* Put data into buffer, sends the data */

UDRn = data;

}

ATMEGA640 Datasheet(PDF) 217 Page - ATMEL Corporation

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