CRC XModem/ZModem解决方案 [英] CRC XModem/ZModem solution

问题描述

我需要计算VB2008中某些电报的CRC，但不确定是X还是Zmodem.老实说，我无法理解该算法，因为我看到了一些带有查询表的表，其他带有策略，移位的表...
我使用的这些电报示例以及CRC计算中使用的数据在0x02和0x04之间(不包括02和04).

STX ADDR数据EOT CRCH CRCL ETX
02 38 51 4D 4E 30 30 23 04 F1 D7 03

02 38 51 4D 4E 31 30 04 EC CC 03

02 38 51 4D 4E 32 30 52 04 27 D7 03

我想知道是否没有流程图解释如何计算CRC，我可以使用的DLL甚至VB中的代码.
如果有人可以帮助我...

问候.

I need to calculate the CRC of some telegrams in VB2008 but not sure if it is X or Zmodem. And honestly I cant understand the algorithm because i''ve seen some with lookup tables, other with polinomes, shifts...
These examples of telegrams i''m using and the data used in the CRC calculation is between 0x02 and 0x04 (02 and 04 excluded).

STX ADDR DATA EOT CRCH CRCL ETX
02 38 51 4D 4E 30 30 23 04 F1 D7 03

02 38 51 4D 4E 31 30 04 EC CC 03

02 38 51 4D 4E 32 30 52 04 27 D7 03

I wonder if there aren''t any flowcharts explaining how to calculate the CRC, or a DLL i can use, or even the code in VB.
If anyone can help me with this...

Regards.

推荐答案

在这里，您是VB函数(非常类似于C的代码:它是人造" 例程，请参见[ ^ ]).
如果效率很重要，请考虑移植基于表的表.

Here you are the VB function (very C-like code: it is a direct porting of the ''ufficial'' C routine, see [^]).
If efficiency matters, consider porting a table-based one.

Function calcrc(ByVal data() As Byte, ByVal count As Integer) As Integer
    Dim crc As Integer = 0
    Dim i, j As Integer
    Dim d As Integer

    For i = 0 To count - 1
        d = data(i)
        crc = crc Xor (d << 8)
        For j = 0 To 7
            If ((crc And &H8000) <> 0) Then
                crc = (crc << 1) Xor &H1021
            Else
                crc = (crc << 1)
            End If
        Next
    Next
    calcrc = crc And &HFFFF
End Function

以下代码是对您的第一批数据的测试:

The following code is a test with your first chunk of data:

Sub Main()
    'Please note data(6) declare 7 items (OK, that's VB madness)
    Dim data(6) As Byte
    Dim crc As Integer
    data(0) = &H38
    data(1) = &H51
    data(2) = &H4D
    data(3) = &H4E
    data(4) = &H30
    data(5) = &H30
    data(6) = &H23
    crc = calcrc(data, 7)
End Sub

:)

:)

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