EX21-2

#include#include#define uchar unsigned char

#define uint unsigned int

uchar rdata;

uchar flag;

void usart_init(void)

{

UCSRC=0X86;

UBRRL=4;//12500BPS

UBRRH=0;

UCSRB=0X98;

SREG |=BIT(7);

}

void usart_send(uchar data)

{

while(!(UCSRA&BIT(5)));

UDR=data;

while(!(UCSRA&BIT(6)));

UCSRA |=BIT(6);

}

#pragma interrupt_handler usartrece:12

void usartrece(void)

{

SREG &=~BIT(7);

rdata=UDR;

flag=1;

SREG |=BIT(7);

}

void main(void)

{

uchar 1='h';

uart_init(9600);

// uart_send(i);

while(1)

{

if(flag)

{

flag=0;

uart_send(rdata);

}

}

}