How to read 64-bit integer data from serial port

Hi,

I work with a piece of hardware that sends data to USB port in an signed 64-bit integer format. I do not know how to read the stream of data with such precision. When I try to read the stream of data using:

X = fread(s, 1, 'long');

The data does not make any sense. I understand that the 'long' precision may be 32 or 64 bit. So I guess in this case it functions as 32-bit. I have though of using 'double' or 'float64' precision but the read data does not make any sense either. Can anybody help me through this problem?

Thanks in advance

Answer 1

[Walter Roberson]

X4 = fread(s, 8, 'uint8');

now re-arrange the byte order to match that used by the sending machine. For example,

X4n = X4([3 4 1 2 7 8 5 6]);  %if that's what the source happens to use

then

X = typecast(X, 'int64');

In the most simple case where the bytes do not have to be rearranged, you can

X = typecast(fread(s, 8, 'uint8'), 'int64');

or for more efficiency,

X = typecast(fread(s, 2, 'uint32'), 'int64');