How to do a Double Byte XOR Checksum?

It might be some parity check. Try to XOR all blocks of 2 bytes and check what you get

Tried it, but still didn't land on the check code given in the packet.

But first, I found that the number of sample points was 9 bytes short in my original packet I was assessing.  The LS value says there should be 40 sample points.  So, I extracted from the stream of serial data a segment that had 80 bytes after the CS packet item.  This should be correct since each sample point is made of two bytes (80/2=40).

In the new packet shown below, the check code is 0x0E63

I made this routine in Excel to process the double byte XORs.  Unfortunately, it gives C7 01 or 0x01C7 in little endian format.

Here's the algorithm:

1. pass a comma delimited string of decimal values representing the original hex data
2. split the string into a string array representing each byte in succession
3. loop through the string array to create two arrays of bytes to process.  The arrays represent a left side column and a right side column to process.
4. loop through the newly formed columns to xor each side
5. present the answer in a message box

I'm wondering if step 4 is where I'm not thinking right on processing it????

Sub doer()
    MsgBox (my_checksum("0,0,182,12,228,12,30,5,29,5,0,0,50,13,0,0,0,0,36,13,4,13,244,12,228,12,216,12,204,12,201,12,185,12,177,12,169,12,165,12,161,12,153,12,153,12,149,12,149,12,145,12,145,12,145,12,145,12,145,12,149,12,157,12,161,12,161,12,165,12,177,12,181,12,193,12,197,12,208,12"))
End Sub
Function my_checksum(str As String) As String
    Dim bytes() As String
    Dim left_byte(100) As Byte
    Dim right_byte(100) As Byte
    Dim left_xor As Byte
    Dim right_xor As Byte
    Dim tt As Integer
    
    bytes = Split(str, ",")
    
    ' tt will index the new byte array we parse
    tt = 0
    ' Convert the strings to integers and then to bytes.  Make a left column and right column to process next with the xor operation
    For ii = 0 To UBound(bytes) - 1 Step 2
        left_byte(tt) = CByte(CInt(bytes(ii)))
        right_byte(tt) = CByte(CInt(bytes(ii + 1)))
        tt = tt + 1
    Next
    
    ' tt will now represent the upper bound of our byte arrays below
    tt = tt - 1
    
    
    left_xor = 0
    right_xor = 0
    
    ' perform the xor operation in double byte fashion
    For ii = 0 To tt
        left_xor = left_xor Xor left_byte(ii)
        right_xor = right_xor Xor right_byte(ii)
    Next
    
    my_checksum = ((Hex(left_xor) & " " & Hex(right_xor)))
End Function

Tried it, but still didn't land on the check code given in the packet.

But first, I found that the number of sample points was 9 bytes short in my original packet I was assessing.  The LS value says there should be 40 sample points.  So, I extracted from the stream of serial data a segment that had 80 bytes after the CS packet item.  This should be correct since each sample point is made of two bytes (80/2=40).

In the new packet shown below, the check code is 0x0E63

I made this routine in Excel to process the double byte XORs.  Unfortunately, it gives C7 01 or 0x01C7 in little endian format.

Here's the algorithm:

1. pass a comma delimited string of decimal values representing the original hex data
2. split the string into a string array representing each byte in succession
3. loop through the string array to create two arrays of bytes to process.  The arrays represent a left side column and a right side column to process.
4. loop through the newly formed columns to xor each side
5. present the answer in a message box

I'm wondering if step 4 is where I'm not thinking right on processing it????

Sub doer()
    MsgBox (my_checksum("0,0,182,12,228,12,30,5,29,5,0,0,50,13,0,0,0,0,36,13,4,13,244,12,228,12,216,12,204,12,201,12,185,12,177,12,169,12,165,12,161,12,153,12,153,12,149,12,149,12,145,12,145,12,145,12,145,12,145,12,149,12,157,12,161,12,161,12,165,12,177,12,181,12,193,12,197,12,208,12"))
End Sub
Function my_checksum(str As String) As String
    Dim bytes() As String
    Dim left_byte(100) As Byte
    Dim right_byte(100) As Byte
    Dim left_xor As Byte
    Dim right_xor As Byte
    Dim tt As Integer
    
    bytes = Split(str, ",")
    
    ' tt will index the new byte array we parse
    tt = 0
    ' Convert the strings to integers and then to bytes.  Make a left column and right column to process next with the xor operation
    For ii = 0 To UBound(bytes) - 1 Step 2
        left_byte(tt) = CByte(CInt(bytes(ii)))
        right_byte(tt) = CByte(CInt(bytes(ii + 1)))
        tt = tt + 1
    Next
    
    ' tt will now represent the upper bound of our byte arrays below
    tt = tt - 1
    
    
    left_xor = 0
    right_xor = 0
    
    ' perform the xor operation in double byte fashion
    For ii = 0 To tt
        left_xor = left_xor Xor left_byte(ii)
        right_xor = right_xor Xor right_byte(ii)
    Next
    
    my_checksum = ((Hex(left_xor) & " " & Hex(right_xor)))
End Function