ATmega64A datasheet(182/392 Pages) ATMEL

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182

8160C–AVR–07/09

ATmega64A

The function simply waits for the transmit buffer to be empty by checking the UDREn 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.

20.6.2

Sending Frames with 9 Data Bits

If 9-bit characters are used (UCSZn = 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.

Note:

1. These transmit functions are written to be general functions. They can be optimized if the con-

tents of the UCSRnB is static. For example, only the TXB8n bit of the UCSRnB Register is

used after initialization.

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 Communi-

cation mode or for other protocol handling as for example synchronization.

20.6.3

Transmitter Flags and Interrupts

The USART Transmitter has two flags that indicate its state: USART Data Register Empty

(UDREn) and Transmit Complete (TXCn). Both flags can be used for generating interrupts.

Assembly Code Example

(1)

USART_Transmit:

; Wait for empty transmit buffer

sbis

UCSRnA,UDREn

rjmp

USART_Transmit

; Copy ninth bit from r17 to TXB8

cbi

UCSRnB,TXB8n

sbrc

r17,0

sbi

UCSRnB,TXB8n

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

out

UDRn,r16

ret

C Code Example

(1)

void

USART_Transmit( unsigned int data )

{

/* Wait for empty transmit buffer */

while

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

;

/* Copy ninth bit to TXB8 */

UCSRnB &= ~(1<<TXB8n);

if ( data & 0x0100 )

UCSRnB |= (1<<TXB8n);

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

UDRn = data;

}

ATmega64A Datasheet(PDF) 182 Page - ATMEL Corporation

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