http://wormfood.net/avrbaudcalc.php
흔히 쓰는
16MHz에 9600bps 라면
UBRR은 103이 된다.
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//http://mulgu.kr/entry/Code-Example-ATMEGA848-UART-%EC%98%88%EC%A0%9C%EC%86%8C%EC%8A%A4
▼ATmega8기준 (수정 필요하면 instructables.tistory.com/64 로 의뢰해주세요)
#define F_CPU 16000000UL // ◀8000000UL == 8 MHz
/* Very Important - change F_CPU to match target clock
타겟 클락에 맞춰서 바꿀것
Note: default AVR CLKSEL is 1MHz internal RC
디폴트는 1MHz 내부 RC이다.
This program transmits continously on USART.
Interrupt is used for
Receive charactor, which is then transmitted instead.
LEDs are used
as a test. Normal RX routine is included but not used.
Change USART_BAUDRATE constant to change Baud Rate
*/
#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>
// Define baud rate
#define USART_BAUDRATE 9600//◀38400
#define BAUD_PRESCALE (((F_CPU / (USART_BAUDRATE * 16UL))) - 1)
// 8000000 / (38400 * 16)
// 8000000 / 614400 = 625/48
// 625/48 - 1 = 577/48 = 12.0208...
volatile unsigned char value;
/* This variable is volatile so both main and RX interrupt can use it.
It could also be a uint8_t type */
/* Interrupt Service Routine for Receive Complete
NOTE: vector name changes with different AVRs see AVRStudio -
Help - AVR-Libc reference - Library Reference - <avr/interrupt.h>: Interrupts
for vector names other than USART_RXC_vect for ATmega32 */
ISR(USART_RXC_vect)
{
value = UDR; //read UART register into value
PORTB = ~value; // output inverted value on LEDs (0=on)
}
void USART_Init(void)
{
// Set baud rate
UBRRL = BAUD_PRESCALE;// Load lower 8-bits into the low byte of the UBRR register
UBRRH = (BAUD_PRESCALE >> 8);
/* Load upper 8-bits into the high byte of the UBRR register
Default frame format is 8 data bits, no parity, 1 stop bit
to change use UCSRC, see AVR datasheet*/
// Enable receiver and transmitter and receive complete interrupt
UCSRB = ((1<<TXEN)|(1<<RXEN) | (1<<RXCIE));
}
void USART_SendByte(uint8_t u8Data)
{
// Wait until last byte has been transmitted
while((UCSRA &(1<<UDRE)) == 0);
// Transmit data
UDR = u8Data;
}
// not being used but here for completeness
// Wait until a byte has been received and return received data
uint8_t USART_ReceiveByte()
{
while((UCSRA &(1<<RXC)) == 0);
return UDR;
}
void Led_init(void)
{
//outputs, all off
DDRB =0xFF;
PORTB = 0xFF;
}
int main(void)
{
USART_Init(); // Initialise USART
sei(); // enable all interrupts
Led_init(); // init LEDs for testing
value = 'A'; //0x41;
PORTB = ~value; // 0 = LED on
for(;;){ // Repeat indefinitely
USART_SendByte(value); // send value
_delay_ms(250);
// delay just to stop Hyperterminal screen cluttering up
}
}
