Configuring the serial Port in Ms Access (1 Viewer)

Dim Start As String
Dim strTMP As String
Dim strLength As String, L As Long, L1 As Integer, L2 As Integer, L3 As Integer, L4 As Integer
Start = Chr(&H1A) & Chr(&H5D)
strData = JsonConverter.ConvertToJson(transaction, Whitespace:=3) & Chr$(13)
L = Len(strData) 'Only length of content string. May be start, length and CRC should be added          L = Len(strData) + 9 (or 7 without CRC)
L1 = L Mod 256
L2 = (L - L1) / 256 Mod 256
L3 = ((L - L1) / 256 - L2) / 256 Mod 256
L4 = (((L - L1) / 256 - L2) / 256 - L3) / 256 Mod 256
strLength = Chr(L4) & Chr(L3) & Chr(L2) & Chr(L1)    
strTMP = Start & strLength & Chr(2) & strData
strTMP = strTMP & strData
' function for CRC calculation see below
strTMP =  strTMP & CRC(strTMP)
lngStatus = CommWrite(intPortID, strTMP)’This is code that will bandle strTMP & CRC(strTMP)

CRC VBA Code:

Option Compare Database
Option Explicit

Public Function CRC8(ByVal AppID As String) As String
    Dim CRC8 As Byte
    Dim i As Integer
    Dim J As Integer
    Dim AppIDarray() As Byte  '<--- explicitly dimensioned as a Byte array to avoid confusion
    Dim aidLength As Long

    CRC8 = &HC7

    'The AppID is actually bytes stored in hexadecimal in a string. You have to convert them back to bytes before you can run a crc8 on them.
    AppIDarray = HexToByte(AppID)
    aidLength = UBound(AppIDarray)
            For J = 0 To aidLength
                CRC8 = CRC8 Xor AppIDarray(J)
                For i = 1 To 8
                    If CRC8 And &H80 Then
                     'masking off the left-most bit before shifting prevents the Overflow error.
                     CRC8 = ((&H7F And CRC8) * 2) Xor &H1D
                    Else
                     CRC8 = CRC8 * 2
                    End If
                Next i
            Next J
    CRC8 = CRC8
End Function
Public Function HexToByte(strHex As String) As Byte()
    Dim i As Integer
    Dim tempByte As Byte
    Dim outBytes() As Byte
    ReDim outBytes(Len(strHex) \ 2 - 1)
    For i = 0 To Len(strHex) \ 2 - 1
    Dim J As Integer
    Dim char As String
        For J = 0 To 1
           char = Mid(strHex, i * 2 + J + 1, 1)
            Select Case char
                Case "0", "1", "2", "3", "4", "5", "6", "7", "8", "9":
                    tempByte = tempByte Or (Asc(char) - 48)
                Case "A", "B", "C", "D", "E", "F":
                    tempByte = tempByte Or (Asc(char) - 55)
            End Select
            If J = 0 Then
                tempByte = tempByte * 2 ^ 4
            Else
                outBytes(i) = tempByte
                tempByte = 0
            End If
        Next
    Next
    HexToByte = outBytes
End Function