ATmega324P datasheet(180/377 Pages) ATMEL

180 / 377 page

180

7674F–AVR–09/09

ATmega164P/324P/644P

Notes:

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 TXB8 bit of the UCSRnB 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 communi-

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

17.7.3

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.

The Data Register Empty (UDREn) Flag indicates whether the transmit buffer is ready to receive

new data. This bit is set when the transmit buffer is empty, and cleared when the transmit buffer

contains data to be transmitted that has not yet been moved into the Shift Register. For compat-

ibility with future devices, always write this bit to zero when writing the UCSRnA Register.

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;

}

ATmega324P Datasheet(PDF) 180 Page - ATMEL Corporation

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