CRC-16 Modbus Calculation

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VB

Hai All,
While i am writing code to calculate CRC16 Modbus. But gives some wrong values. Can any one correct me .......
Here is my code.... my input is ASCII value

Public Function getCRC16(ByVal strInput As String)
        Dim lngCheck As Long
        Dim Power(7) As Integer
        Dim I As Integer
        Dim J As Integer
        Dim Poly As Long
        Dim CRC As Long
        Dim TestBit As Boolean
        Dim TestBit1 As Boolean
        Dim TestBit2 As Boolean

        Poly = &H1021
        CRC = &HFFFF

        For J = 0 To 7
            Power(J) = 2 ^ J
        Next J

        For I = 1 To Len(strInput) Step 2
            lngCheck = Val("&H" & Mid$(strInput, I, 2))
            For J = 7 To 0 Step -1
                If (CRC And 32768) = 32768 Then
                    TestBit1 = True
                Else
                    TestBit1 = False
                End If

                If (lngCheck And Power(J)) = Power(J) Then
                    TestBit2 = True
                Else
                    TestBit2 = False
                End If

                TestBit = TestBit1 Xor TestBit2
                CRC = (CRC And 32767) * 2
                If TestBit = True Then
                    CRC = CRC Xor Poly
                End If

            Next J
        Next I

        Dim tmp As String
        tmp = Hex(CRC)
        getCRC16 = tmp
        MsgBox(tmp)
    End Function