LSB first or MSB first ?

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I want to convert a decimal number in hexadecimal number and send through serial port with LSB first.

I tried this

C#

Int32 decValue = 1234056789;
byte[] testBytes = new byte[4];

    testBytes [0] = (byte)(decValue & 0x000000FF);
    testBytes [1] = (byte)((decValue >> 8) & 0x000000FF);
    testBytes [2] = (byte)((decValue >> 16) & 0x000000FF);
    testBytes [3] = (byte)((decValue >> 24) & 0x000000FF);

Is testBytes[0] contains bytes in LSB first or MSB first???

Posted 24-Mar-14 19:33pm

DoingWork

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Sergey Alexandrovich Kryukov · Answer 1 · 2014-03-24T19:43:00

Solution 1

Strictly speaking, it depends on the requirements of the device connected to the other end of your RS-232 cable. Windows uses "little-endian" formats (least significant byte goes first); I would say, most systems do the same. However, this is not a rule; "big-endian" is also used. For example, so-called standard "network order" is big-endian.

Please see: http://en.wikipedia.org/wiki/Endianness[^].

—SA

Posted 24-Mar-14 19:43pm

Sergey Alexandrovich Kryukov

Updated 24-Mar-14 19:50pm

v3

Comments

DoingWork 25-Mar-14 1:58am

Thanks for reply.
I want to know only that to send LSB first, Whether I should send testBytes[0] first or testBytes[3] first ?????

Sergey Alexandrovich Kryukov 25-Mar-14 2:56am

Didn't I just answer? Look at what the other device require and do it.
—SA

User 59241 · Answer 2 · 2014-03-24T20:25:00

This is the way to test taken from msdn: http://msdn.microsoft.com/en-us/library/bb384066.aspx[^]

C#

byte[] bytes = { 0, 0, 0, 25 };

int i = BitConverter.ToInt32(bytes, 0);
Console.WriteLine("int: {0}", i);

If this prints 25 then your computer is big-endian - you send testBytes [3] first.
If it does not print 25 then send testBytes [0] first.

There is however a test for endian_ness BitConverter.IsLittleEndian. So you can write:

C#

byte[] bytes = { 0, 0, 0, 25 };

// If the system architecture is little-endian (that is, little end first), 
// reverse the byte array. 
if (BitConverter.IsLittleEndian)
    Array.Reverse(bytes);

int i = BitConverter.ToInt32(bytes, 0);
Console.WriteLine("int: {0}", i);
// Output: int: 25

You should also look at BitConverter.GetBytes(Int32) for converting Int32 to byte array.
http://msdn.microsoft.com/en-us/library/de8fssa4(v=vs.110).aspx[^]