ATmega32A datasheet(156/352 Pages) ATMEL

156 / 352 page

156

8155B–AVR–07/09

ATmega32A

Note:

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

tents of the UCSRB is static. (i.e., only the TXB8 bit of the UCSRB Register is used after

initialization).

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.

19.6.3

Transmitter Flags and Interrupts

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

(UDRE) and Transmit Complete (TXC). Both flags can be used for generating interrupts.

The Data Register Empty (UDRE) 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 UCSRA Register.

When the Data Register empty Interrupt Enable (UDRIE) bit in UCSRB is written to one, the

USART Data Register Empty Interrupt will be executed as long as UDRE is set (provided that

global interrupts are enabled). UDRE is cleared by writing UDR. When interrupt-driven data

transmission is used, the Data Register Empty Interrupt routine must either write new data to

UDR in order to clear UDRE or disable the Data Register empty Interrupt, otherwise a new inter-

rupt will occur once the interrupt routine terminates.

Assembly Code Example(1)

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)

void

USART_Transmit( unsigned int data )

{

/* Wait for empty transmit buffer */

while

( !( UCSRA & (1<<UDRE))) )

;

/* Copy 9th bit to TXB8 */

UCSRB &= ~(1<<TXB8);

if ( data & 0x0100 )

UCSRB |= (1<<TXB8);

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

UDR = data;

}

ATmega32A Datasheet(PDF) 156 Page - ATMEL Corporation

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