ATmega32A datasheet(155/352 Pages) ATMEL

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8155B–AVR–07/09

ATmega32A

The following code examples show a simple USART transmit function based on polling of the

Data Register Empty (UDRE) Flag. When using frames with less than eight bits, the most signif-

icant bits written to the UDR are ignored. The USART has to be initialized before the function

can be used. For the assembly code, the data to be sent is assumed to be stored in Register

R16

Note:

1. See “About Code Examples” on page 6.

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

19.6.2

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.

Assembly Code Example

(1)

USART_Transmit:

; Wait for empty transmit buffer

sbis

UCSRA,UDRE

rjmp

USART_Transmit

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

out

UDR,r16

ret

C Code Example(1)

void

USART_Transmit( unsigned char data )

{

/* Wait for empty transmit buffer */

while

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

;

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

UDR = data;

}

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