AVR Serial.c

serial.h

/* ************************************************************************* */
/*                                                                           */
/* Description       : Header file for serial.c                              */
/*                     Based on AppNote AVR109 - Self-programming            */
/*                                                                           */
/* FileName          : serial.h                                              */
/* Compiler          : AVR-GCC/avr-libc(>= 1.2.5), TODO: IAR C 3.10C         */
/* Revision          : 1.7                                                   */
/* Date              : 30. November 2008                                     */
/* Updated by        : Richard Balogh                                        */
/* Target platform   : ATmega88, TODO: All AVRs with bootloader support      */
/*                                                                           */
/* ************************************************************************* */

         void initbootuart( void );
         void sendchar( unsigned char );
unsigned char recchar( void );

serial.c

/* ************************************************************************* */
/*                                                                           */
/* Description       : UART communication routines                           */
/*                     Based on AppNote AVR109 - Self-programming            */
/*                                                                           */
/* FileName          : serial.h                                              */
/* Compiler          : AVR-GCC/avr-libc(>= 1.2.5), TODO: IAR C 3.10C         */
/* Revision          : 1.7                                                   */
/* Date              : 30. November 2008                                     */
/* Updated by        : Richard Balogh                                        */
/* Target platform   : ATmega88, TODO: All AVRs with bootloader support      */
/*                                                                           */
/* ************************************************************************* */

#include <avr\io.h>

/* baud rate register value calculation */
#define	CPU_FREQ	18432000UL      // If CKDIV8 checked, then /8!
#define	BAUD_RATE	9600
                             // BAUD = f / 16 * (UBR+1) alebo UBR = CPUFREQ/16/BAUD_RATE-1
#define	BRREG_VALUE	119  // hodnota z tabulky v datashhete pre 18,4320MHz, 2x=0, 9600Baud, error = 0%    


/* definitions for UART control */      // upravene pre ATmega88
#define	BAUD_RATE_LOW_REG	UBRR0L  // ??? (Staci Low Byte, < 255 )
#define	UART_CONTROL_REG_B	UCSR0B  // OK, checked
#define	ENABLE_TRANSMITTER_BIT	TXEN0   // OK, checked
#define	ENABLE_RECEIVER_BIT	RXEN0   // OK, checked
#define	UART_STATUS_REG		UCSR0A  // OK, checked (but also control reg.)
#define DATA_REGISTER_EMPTY_BIT UDRE0   // Added, for possible speed-up
#define	TRANSMIT_COMPLETE_BIT	TXC0    // OK, checked
#define	RECEIVE_COMPLETE_BIT	RXC0    // OK, checked
#define UART_CONTROL_REG_C      UCSR0C  // Added for mode setting
#define	UART_DATA_REG		UDR0    // OK, checked



void initbootuart(void)
{
  BAUD_RATE_LOW_REG = BRREG_VALUE;                 // OK, preddelic pre 9600
                                                   // bit 2x = 0
  UART_CONTROL_REG_C = (1<<UCSZ01)|(1<<UCSZ00);    // Added: Async. UART, None 
                                                   // Parity, 8-data, 1 stopbit
  UART_CONTROL_REG_B = (1 << ENABLE_RECEIVER_BIT)|
                    (1 << ENABLE_TRANSMITTER_BIT); // enable receive + transmit 
                                                   
}


void sendchar(unsigned char c)
{
  UART_DATA_REG = c;                                   // prepare transmission
  while (!(UART_STATUS_REG & (1 << TRANSMIT_COMPLETE_BIT)));// wait until byte sendt
  UART_STATUS_REG |= (1 << TRANSMIT_COMPLETE_BIT);          // delete TXCflag
}


unsigned char recchar(void)
{
  while( !(UART_STATUS_REG & (1 << RECEIVE_COMPLETE_BIT)) );  // wait for data
  return UART_DATA_REG;
}

main.c

#include <avr\io.h>
#include "serial.h"              // Nasa kniznica... 

int main(void) 
{
 char c;
 
 initbootuart();
 sendchar('O');
 sendchar('K');
 sendchar('\n');

 for (c=32;c<=127;c++) 
   sendchar(c);

 for (;;) {
     /* Do nothing */
          }
}