Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!


Urgent help :CRC-CCITT help needed

syncazzysyncazzy Member Posts: 4
i am developing a VB code to generate CRC-CCITT for my data frame
which is
(0x01 0x10 0x01 0x20 0x02 0xF0 0x04 0x02 0x23 0x10 0x63 0x02 0x03 0xFA 0x33 0x04)
so if i send 0x01 0x10 0x01 0x20 0x02 0xF0 0x04 0x02 0x23 0x10 0x63 0x02 0x03 to a crc-ccitt function i should get crc 0xFA 0x33 which i will add to my data and put an end of header then send via comm port

this what have tried but i am not getting 0xFA 0x33 as required by the protocol

'test with this hex string 0110012002F004022310630203 i am suppossed to get crc FA33
' Or testing with 0110012016F004022310590203 should give crc 5F06
' CRC-CCITT Polynomial: 1021h = x16 + x12 + x5 + 1 (LSB first mode)Start value: FFFFh

Private Sub CommandButton1_Click()
Dim crc As Long
Dim n As String
Dim values(13) As Byte
Dim k As Integer
Dim i As Integer

crc = &HFFFF&
n = text1.Text

k = 0
For i = 1 To Len(n)
values(k) = "&H" & Mid(n, i, 2)
i = i + 1
k = k + 1
Next i

For k = 0 To 12
crc = calc_crc(crc, values(k))
Next k
MsgBox ("Crc " & Hex(crc))

End Sub

Private Function calc_crc(ByVal crc_buff As Long, ByVal inp As Byte) As Long
Dim i As Integer
Dim x16 As Long
Dim values(13) As Byte
For i = 0 To 12

If ((crc_buff And 1) Xor (inp And 1)) = 1 Then
x16 = &H8408&
x16 = 0
End If
crc_buff = crc_buff 2
crc_buff = crc_buff Xor x16
inp = inp 2
Next i
calc_crc = crc_buff
End Function

please urgent
Sign In or Register to comment.