Chapter 6: C Functions and Program Structures

Save this file as Demonstrator.c.

PC_Comm

The next two programs, PC_Comm.h and PC_Comm.c can be copied from the CD to the CommDemo directory, or if you want a preview of coming attractions, you can open a new C/C++ file in Programmer’s Notepad and write:

// PC_Comm.h #include <avr/io.h>

#include <avr/interrupt.h> #include <avr/delay.h>

#include <stdlib.h>

#include "Demonstrator.h"

void OSCCAL_calibration(void) ; void USARTinit(void);

char isCharAvailable(void); char receiveChar(void); void sendChar(char ) ;

void sendString(char *);

Save this file as PC_Comm.h.

In Programmer’s Notepad open a new C/C++ file and write:

// PC_Comm.c

#include "PC_Comm.h"

int main(void)

{

char string[64]; unsigned char count = 0;

// run the initialization routine initializer();

//Begin forever chatting with the PC for(;;)

{

// Check to see if a character is waiting if( isCharAvailable() == 1 )

{

//If a new character is received, get it string[count++] = receiveChar();

//receive a packet up to 64 bytes long

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Chapter 6: C Functions and Program Structures

if(string[count-1] == '\n')// HyperTerminal string ends with \r\n

{

string[count-2] = '\0'; //convert to a string parseInput(string);

string[0] = '\0'; count = 0;

}

else if(count > 64)

{

count = 0; string[0] = '\0';

sendString("Error - received > 64 characters");

}

}

}

return 0;

}

char isCharAvailable()

{

//Does the RX0 bit of the USART Status and Control Register

//indicate a char has been received?

if ( (UCSR0A & (0x80)) ) return 1; else return 0;

}

char receiveChar()

{

// Return the char in the UDR0 register return UDR0;

}

void sendChar(char data)

{

int i = 0;

//To send data with the USART put the data in the USART data register UDR0 = data;

//Check to see if the global interrupts are enabled

if(SREG & 0x80)

{

// Wait until the byte is sent or we count out while ( !(UCSR0A&0x40) && (i<10000) )

{

i++;

}

}

else // Wait until the byte is sent while( !(UCSR0A&0x40) );

// Clear the TXCflag UCSR0A=UCSR0A|0x40;

}

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Chapter 6: C Functions and Program Structures

void sendString(char s[])

{

int i = 0;

while(i < 64) // don't get stuck if it is a bad string

{

if( s[i] == '\0' ) break; // quit on string terminator sendChar(s[i++]);

}

}

void USARTinit()

{

// Increase the oscillator to 2 Mhz for the 19200 baudrate: CLKPR = (1<<CLKPCE); // set Clock Prescaler Change Enable

//set prescaler = 4, Inter RC 8Mhz / 4 = 2Mhz CLKPR = (1<<CLKPS1);

//Set the USART baudrate registers for 19200 UBRR0H = 0;//(unsigned char)(baudrate>>8); UBRR0L = 12;//(unsigned char)baudrate;

//Enable 2x speed change

UCSR0A = (1<<U2X0);

// Enable receiver and transmitter

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Chapter 6: C Functions and Program Structures

while((ASSR & 0x01) | (ASSR & 0x04));

// wait for external crystal to stabilise for(int i = 0; i < 10; i++)

_delay_loop_2(30000);

while(!calibrate)

{

cli(); // mt __disable_interrupt(); // disable global interrupt

TCCR1B = 0; // stop timer1

sei(); // __enable_interrupt(); // enable global interrupt

if ( (TIFR1 && (1<<TOV1)) )

{

}

else

{// read out the timer1 counter value tempL = TCNT1L;

temp = TCNT1H;

temp = (temp << 8);

temp += tempL;

}

if (temp > 6250)

{

OSCCAL--; // the internRC oscillator runs to fast, decrease the OSCCAL

}

else if (temp < 6120)

{

OSCCAL++; // the internRC oscillator runs to slow, increase the OSCCAL

}

else

TCCR1B = (1<<CS10); // start timer1

}

}

Save this file as PC_Comm.c.

Finally make these changes to the makefile:

105