I have several examples in my book (see below). There are dozens of such error detection/retransmission protocols. If both match, then the data packet is considered to be complete and error free. It then extracts the data packet and uses the same algorithm to recalculate theįCS and then compares that local FCS to the one that had been received from the sender. First it looks for the header, then looks for the ending details, including the FCS that was sent. Upon receipt, the receiving program buffers data and parses it. So, the general process is to create a data packet, calculate the FCS for that packet, add the header and ending details (including the FCS). The data between the start and end are what the FCS algorithm is used to validate. Each frame will be started with a start sequence (header) and terminated by an end sequence, which will Rather, it is used to determine if there has been an error in the transmission. The FCS is not used to distinguish frames. Public Const FCSINIT32 As Long = &HFFFFFFFFL Public Const FCSINIT16 As Integer = &HFFFF UFcs32 = (uFcs32 > 8) Xor fcs32tab((uFcs32 Xor pBuffer(i)) And &HFF)Įnd Sub Public Shared Sub fcs32_final( ByVal uFcs32 As UInteger)Įnd Sub End Class Partial Friend NotInheritable Class DefineConstants Public Shared Sub fcs32_init( ByVal uFcs32 As UInteger)Įnd Sub Public Shared Sub fcs32_update( ByVal uFcs32 As UInteger, ByVal pBuffer() As Byte, ByVal uBufSize As UInteger) ' - ' ' FCS-16 algorithm implemented as described in RFC 1331 #Const FCSINIT16 = True #Const FCSINIT32 = True ' Fast 16 bit FCS lookup table Public Shared fcs16tab() As UShort =
#SV4 CHECKSUM CALCULATOR SOFTWARE#
' ' This software is provided 'as is' with no explicit or implied warranties ' in respect of its properties, including, but not limited to, correctness ' and/or fitness for purpose. ' 'ĝistributed under the terms of the GNU General Public License v2. ' ' - 'Ĝopyright (c) 2003, Dominik Reichl, Germany.
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