Rainbow-electronics ATmega8515L Bedienungsanleitung PDF herunterladen (Seite 137)

137

ATmega8515(L)

2512A–AVR–04/02

If used, the paritybit islocatedbetween the last data bit andfirst stopbit of a serial

frame.

USART Initialization The USART has to beinitializedbeforeanycommunication can take place. Theinitial-

ization process normally consists ofsetting the baudrate,setting frame format and

enabling thetransmitter or theReceiverdepending on theusage. For interrupt driven

USART operation, theglobal interrupt flag should be cleared(and interrupts globally dis-

abled) when doing theinitialization.

Before doing a re-initialization withchangedbaudrate orframe format,be surethat

thereare no ongoing transmissionsduring the period the registers are changed.The

TXC flag can beused to check that theTransmitterhascompleted all transfers, and the

RXC flag can beused to check that therearenounreaddatainthe receive buffer. Note

that theTXC flag must be clearedbeforeeach transmission (before UDRiswritten) if it

is usedfor thispurpose.

The following simple USART initialization codeexamplesshow one assembly and one

Cfunction that areequal in functionality.Theexamples assume asynchronous opera-

tion using polling (no interrupts enabled) and a fixedframe format. The baudrate is

given as a function parameter. For theassembly code, the baudrate parameter is

assumed to be stored in the r17:r16registers. When the function writes to the UCSRC

and UCSRC.

Note: 1. Theexample codeassumes that the part specificheaderfileis included.

Moreadvanced initialization routinescan bemadethat include frame format asparame-

ters, disableinterrupts andso on. However, many applications useafixedsetting of the

baud andcontrolregisters, andfor thesetypes of applications theinitialization code can

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

CCode 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);

}

1 2 ... 132 133 134 135 136 137 138 139 140 141 142 ... 222 223

Kommentare zu diesen Handbüchern

Keine Kommentare

Rainbow-electronics ATmega8515L Bedienungsanleitung Seite 137

Kommentare zu diesen Handbüchern

Verwandte Produkte und Handbücher für Sensoren Rainbow-electronics ATmega8515L