I2C + Excel (Graphic plot with PLX-DAQ)

I’m trying to plot graphics from an IR thermomether MLX90614 into Excel using a parallax plugin (PLX-DAQ) but I got some problems with the code, there some kind of conflict in the communication between I2C and Excel.

Actually the PLX-DAQ reads the Port but doesn’t plot the data into the sheet.

Here’s the code:

#include <i2cmaster.h>

void setup(){
	Serial.println("IR Thermometer plot...");

	i2c_init(); //Initialise the i2c bus
	PORTC = (1 << PORTC4) | (1 << PORTC5);//enable pullups

void loop(){
    int dev = 0x5A<<1;
    int data_low = 0;
    int data_high = 0;
    int pec = 0;
    // read
    data_low = i2c_readAck(); //Read 1 byte and then send ack
    data_high = i2c_readAck(); //Read 1 byte and then send ack
    pec = i2c_readNak();
    //This converts high and low bytes together and processes temperature, MSB is a error bit and is ignored for temps
    double tempFactor = 0.02; // 0.02 degrees per LSB (measurement resolution of the MLX90614)
    double tempData = 0x0000; // zero out the data
    int frac; // data past the decimal point
    // This masks off the error bit of the high byte, then moves it left 8 bits and adds the low byte.
    tempData = (double)(((data_high & 0x007F) << 8) + data_low);
    tempData = (tempData * tempFactor)-0.01;
    float celcius = tempData - 273.15;
    float fahrenheit = (celcius*1.8) + 32;

    Serial.print("Celcius: ");

    //Serial.print("Fahrenheit: ");

    delay(300); // wait a second before printing again


I hope you can help me, thank you all