Whereas before you were sending the integer encoded as a string, you're now sending the integer bytes. It's a different function to send, and thus a different function to read. You want to use fread:
t.ByteOrder = littleEndian; %see comment below
value = fread(t, 1, 'uint16') %assuming your integer is unsigned. Otherwise use 'int16'.
Make sure that the ByteOrder property of your connection is set correctly for the order you send the bytes in. If you send first_part first, then you're using littleEndian. Otherwise, you're using bigEndian.
My example assumes an unsigned 16-bit (2-bytes) integer, that is it's in the range 0-65535. If your integer is actually signed (in the range [-32678, +32767]), then use 'int16'.
