msaynevirta / GPS tracker - Files

i2c.c
#include "i2c.h"
#include <avr/io.h>
/* Define bit rate */
#define SCL_CLK F_CPU/(16+ 2(TWBR)*pow(4,TWPS0)
#define BITRATE(TWSR) ((F_CPU/SCL_CLK)-16)/(2*pow(4,(TWSR&((1<<TWPS0)|(1<<TWPS1)))))


int I2C_transmit(char data) 
{

TWCR = (1<<TWINT)|(1<<TWSTA)|(1<<TWEN); // Enable TWI, Send START condition
while (!(TWCR & (1<<TWINT)));   // Wait for TWINT Flag set. This indicates that the START condition has been transmitted
if ((TWSR & 0xF8) != 0x08) {return 0;} // Check value of TWI Status Register. Mask prescaler bits. If status different from START then return 0
TWDR = data; //  Write SLA+W in TWI data register
TWCR = (1<<TWINT) | (1<<TWEN); // Load SLA_W into TWDR Register. Clear TWINT bit in TWCR to start transmission of address
while (!(TWCR & (1<<TWINT)));  // Wait for TWINT Flag set. This indicates that the SLA+W has been transmitted, and ACK/NACK has been received

if ((TWSR & 0xF8) != TWEA) {return 0;}  // Check value of TWI Status Register. Mask prescaler bits. If status different from ack bit then return 0
TWDR = 0x18;
TWCR = (1 << TWINT) | (1 << TWEN); // Load DATA into TWDR Register. Clear TWINT bit in TWCR to start transmission of data

while (!(TWCR & (1 << TWINT))); // Wait for TWINT Flag set. This indicates that the DATA has been transmitted, and ACK/NACK has been received.
if ((TWSR & data) != TWEA) {return 0;} // Check value of TWI Status Register. Mask prescaler bits. If status different from MT_DATA_ACK then return 0
TWCR = (1 << TWINT)|(1 << TWEN)|(1 << TWSTO); // Transmit STOP condition

}
char I2C_receive()
{
    TWCR = (1 << TWEN) |(1 << TWINT)|(1 << TWEA); // Enable TWI, generation of ack
    while(!(TWCR&(1 << TWINT)));	// Wait until TWI finish its current job
    return TWDR;			// Return received data 
}

void I2C_Init()			// I2C initialize function
{
    TWBR = BITRATE(TWSR=0x00);	// Get bit rate register value by formula 
}


int main(void)
{
    I2C_Init();
    for(;;) // continuous loop
    {
       char ReceivedData = I2C_receive();
       I2C_transmit(ReceivedData);
    }
    
}