INFICON SQM-160 Thin Film Deposition Monitor - Manual (Page 72)

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SQM-160 Operating Manual
5.5 CRC Examples
In this section you will find examples of code for calculating the CRC in Visual
Basic, Java, and C++. Instructions for calculating the CRC are located in
section
5.3 on page 5-6 .
5.5.1 Visual Basic ® 5/6
Public Sub CalcChkSumByte(ByRef ByData() As Byte, ByRef byCRC() As
Byte)
Dim CRC As Integer
Dim TmpCRC As Integer
Dim LastIndex As Long
Dim i As Integer
Dim j As Integer
LastIndex = UBound(ByData())
' Avoid on length messages
If ByData(1) > 0 Then
' Set 14 bit CRC to all ones
CRC = &H3FFF
For j = 1 To LastIndex - 2
' XOR current character with CRC
CRC = CRC Xor ByData(j)
' Go thru lower 8 bits of CRC
For i = 1 To 8
' Save CRC before shift
TmpCRC = CRC
' Shift right one bit
CRC = Shri(CRC, 1)
If (TmpCRC And 1) = 1 Then
' If LSB is 0 (before shift), XOR with hex 2001
CRC = CRC Xor &H2001
End If
Next i
Next j
' Be sure we still have 14 bits
CRC = CRC And &H3FFF
byCRC(0) = (LoByte(CRC) And &H7F) + 34
byCRC(1) = (LoByte(Shri(CRC, 7)) And &H7F) + 34
Else
' Empty message
byCRC(0) = 0
byCRC(1) = 0
End If