Modbus通信VB源程序.doc

用Visual Basic编写的Modbus 通信源程序 以下是PC机与PLC进行Modbus通信的VB源程序，提供给大家做个参考。 1） 模块文件：modCRC，其中包含了CRC校验的函数。 data 待校验的数组名称 no 数组中元素个数 btLoCRC 算出的CRC高字节 btHiCRC 算出的CRC低字节 Public Function CalCRC16Fast(data() As Byte, no As Integer, btLoCRC As Byte, btHiCRC As Byte) As String Dim CL As Byte, CH As Byte 多项式码HA001 Dim SaveHi As Byte, SaveLo As Byte Dim i As Integer Dim Flag As Integer btHiCRC = HFF btLoCRC = HFF CL = H1 CH = HA0 For i = 0 To (no - 1) btHiCRC = btHiCRC Xor data(i) 每一个数据与CRC寄存器进行异或 For Flag = 0 To 7 SaveHi = btLoCRC SaveLo = btHiCRC btLoCRC = btLoCRC \ 2 高位右移一位 btHiCRC = btHiCRC \ 2 低位右移一位 If ((SaveHi And H1) = H1) Then 如果高位字节最后一位为1 btHiCRC = btHiCRC Or H80 则低位字节右移后前面补1 End If 否则自动补0 If ((SaveLo And H1) = H1) Then 如果LSB为1，则与多项式码进行异或 btLoCRC = btLoCRC Xor CH btHiCRC = btHiCRC Xor CL End If Next Flag Next i Dim ReturnData(1) As Byte ReturnData(0) = btHiCRC CRC高位 ReturnData(1) = btLoCRC CRC低位 CalCRC16Fast = ReturnData End Function Public Function CalCRC16Tbl(data() As Byte, no As Integer, btLoCRC As Byte, btHiCRC As Byte) As String Dim btLoCRC As Byte Dim btHiCRC As Byte btLoCRC = HFF btHiCRC = HFF Dim i As Integer Dim iIndex As Long For i = 0 To (no - 1) iIndex = btHiCRC Xor data(i) btHiCRC = btLoCRC Xor GetCRCLo(iIndex) 低位处理 btLoCRC = GetCRCHi(iIndex) 高位处理 Next i Dim ReturnData(1) As Byte ReturnData(0) = btHiCRC CRC高位 ReturnData(1) = btLoCRC CRC低位 CalCRC16Tbl = ReturnData End Function CRC低位字节值表 Function GetCRCLo(Ind As Long) As Byte GetCRCLo = Choose(Ind