Can't specify machineformat when using fread with a serial object

I am currently gathering real-time data through a serial port object.

To do so, I set up a serial object, and use the callback to run an fread() command. I would like to read it in big-endian format by setting the machineformat parameter using 'b'.

If I read in binary data from a file, I can successfully use the command:

    data=fread(fid, 1, 'uint16',0,'b');

However when I run the same syntax on data from a serial object, I get the error that there are "too many inputs". I currently get around it by using little-endian and the swapbyte() function, however that seems very inefficient.

Below is my code. If anyone has any reasons as to why this error is occurring, I would greatly appreciate the help.

function serial()

s = serial ('COM3');

s.BytesAvailableFcnCount = 2000;
s.BytesAvailableFcnMode = 'byte';
s.BytesAvailableFcn= @callbacktest;

set (s, 'BaudRate', 115200, 'InputBufferSize', 2000, 'OutputBufferSize', 2000);
fopen (s);

function callbacktest(obj, event)
data=fread(obj, 1, 'uint16',0,'b');

Thanks so much for your help!