Converting ADC data to voltage

I am trying to manipulate the data received from my TI ADS1220 using Arduino and MATLAB. I get readings from the Arduino (using arduino toolbox) in the form of 3 bytes in 2's complement form (MSB, DATA, LSB).

I need to shift these bytes into a larger byte and then convert that to a voltage. Here is what I have tried when combining the bytes. From the examples I looked out it looks like I want to shift this into a 32 bit number but I'm not exactly sure why.

[bit]=  writeRead(ADS1220, [RDATA,hex2dec('FF'), hex2dec('FF'),hex2dec('FF')]);

bit(:,1) =[]; %delete first bit

voltage = double(bitor((bitshift(uint8(dec2bin(bit(1))), 8)), bit(2)));
voltage2 = double(bitor((bitshift(voltage, 8)), bit(3)));

Answer 1

[ECEdesigner]

Resolved issue