Rainbow-electronics Atmega169L Bedienungsanleitung PDF herunterladen (Seite 156)

156

ATmega169V/L

2514A–AVR–08/02

The following simple USART initialization code examples show one assembly and one

C function that are equal in functionality. The examples assume asynchronous opera-

tion using polling (no interrupts enabled) and a fixed frame format. The baud rate is

given as a function parameter. For the assembly code, the baud rate parameter is

assumedtobestoredinther17:r16Registers.

Note: 1. The example code assumes that the part specific header file is included.

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”.

More advanced initialization routines can be made that include frame format as parame-

ters, disable 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.

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<<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<<USBS)|(3<<UCSZ0);

}

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