ATmega32A datasheet(154/352 Pages) ATMEL

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154

8155B–AVR–07/09

ATmega32A

Note:

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

More advanced initialization routines can be made that include frame format as parameters, dis-

able interrupts and so on. However, many applications use a fixed setting of the Baud and

Control Registers, and for these types of applications the initialization code can be placed

directly in the main routine, or be combined with initialization code for other I/O modules.

19.6

Data Transmission – The USART Transmitter

The USART Transmitter is enabled by setting the Transmit Enable (TXEN) bit in the UCSRB

den by the USART and given the function as the transmitter’s serial output. The baud rate, mode

of operation and frame format must be set up once before doing any transmissions. If synchro-

nous operation is used, the clock on the XCK pin will be overridden and used as transmission

clock.

19.6.1

Sending Frames with 5 to 8 Data Bit

A data transmission is initiated by loading the transmit buffer with the data to be transmitted. The

CPU can load the transmit buffer by writing to the UDR I/O location. The buffered data in the

transmit buffer will be moved to the Shift Register when the Shift Register is ready to send a new

frame. The Shift Register is loaded with new data if it is in idle state (no ongoing transmission) or

immediately after the last stop bit of the previous frame is transmitted. When the Shift Register is

loaded with new data, it will transfer one complete frame at the rate given by the Baud Register,

U2X bit or by XCK depending on mode of operation.

Assembly Code Example

(1)

USART_Init:

; Set baud rate

out

UBRRH, r17

out

UBRRL, r16

; Enable receiver and transmitter

ldi

r16, (1<<RXEN)|(1<<TXEN)

out

UCSRB,r16

; Set frame format: 8data, 2stop bit

ldi

r16, (1<<URSEL)|(1<<USBS)|(3<<UCSZ0)

out

UCSRC,r16

ret

C Code Example

(1)

void

USART_Init( unsigned int baud )

{

/* Set baud rate */

UBRRH = (unsigned char)(baud>>8);

UBRRL = (unsigned char)baud;

/* Enable receiver and transmitter */

UCSRB = (1<<RXEN)|(1<<TXEN);

/* Set frame format: 8data, 2stop bit */

UCSRC = (1<<URSEL)|(1<<USBS)|(3<<UCSZ0);

}

ATmega32A Datasheet(PDF) 154 Page - ATMEL Corporation

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