understanding MSB LSB - c

Question

I am working on converting a program that runs on a specific micro-controller and adapt it to run on the raspberry pi. I have successfully been able to pull values from the sensor I have been working with but now I have run into a problem and I think it is caused by a few lines of code I am having trouble understanding. I have read up on what they are but am still scratching my head. The code below I believe is supposed to modify the number that gets stored in the X,Y,Z variables however I don't think this is occurring in my current program. Also I had to change byte to an INT to get the program to compile with out errors. This is the unmodified code from the original code I have converted. Can someone tell me if this is even modifying the number in anyway?
void getGyroValues () {
byte MSB, LSB;
MSB = readI2C(0x29);
LSB = readI2C(0x28);
x = ((MSB << 8) | LSB);
MSB = readI2C(0x2B);
LSB = readI2C(0x2A);
y = ((MSB << 8) | LSB);
MSB = readI2C(0x2D);
LSB = readI2C(0x2C);
z = ((MSB << 8) | LSB);
}
Here is the original readI2C function:
int readI2C (byte regAddr) {
Wire.beginTransmission(Addr);
Wire.write(regAddr); // Register address to read
Wire.endTransmission(); // Terminate request
Wire.requestFrom(Addr, 1); // Read a byte
while(!Wire.available()) { }; // Wait for receipt
return(Wire.read()); // Get result
}

Answer 1

I2C is a 2-wire protocol used to talk to low-speed peripherals.
Your sensor should be connected over the I2C bus to your CPU. And you're reading 3 values from the sensor - x, y and z. The values for these are accessible from the sensor as 6 x 8-bit registers.
x - Addresses 0x28, 0x29
y - Addresses 0x2A, 0x2B
z - Addresses 0x2C, 0x2D
ReadI2C() as the function name implies, reads a byte of data from a given address from your sensor and returns the data being read. The code in ReadI2C() is dependent on how your device's I2C controller is setup.
A byte is 8-bits of data. The MSB (Most-Significant-Byte) and LSB(Least-Significant-Byte) denote 8-bits each read over I2C.
It looks like you're interested in a 16-bit data (for x, y and z). To construct the 16-bit data from the 2 pieces of 8-bit data, you shift the MSB by 8-bits to the left and then perform a logical-OR operation with the LSB.
For example:
Let us assume: MSB = 0x45 LSB = 0x89
MSB << 8 = 0x4500
(MSB << 8) | LSB = 0x4589
Look at my comments inline as well:
void getGyroValues () {
byte MSB, LSB;
MSB = readI2C(0x29);
LSB = readI2C(0x28);
// Shift the value in MSB left by 8 bits and OR with the 8-bits of LSB
// And store this result in x
x = ((MSB << 8) | LSB);
MSB = readI2C(0x2B);
LSB = readI2C(0x2A);
// Do the same as above, but store the value in y
y = ((MSB << 8) | LSB);
MSB = readI2C(0x2D);
LSB = readI2C(0x2C);
// Do the same as above, but store the value in z
z = ((MSB << 8) | LSB);
}