modbus.bas

modbus 协议通讯程序

Attribute VB_Name = "modbus"
Option Explicit

Public ReceiveData() As Byte


Function CRC16(ByRef data() As Byte) As String
  Dim ArraySize As Integer
      Dim CRC16Lo As Byte, CRC16Hi As Byte      'CRC寄存器
      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
      CRC16Lo = &HFF
      CRC16Hi = &HFF
      CL = &H1
      CH = &HA0
      
      ArraySize = UBound(data) - LBound(data)
      ReDim ReturnData(ArraySize + 2) As Byte
     
      For i = LBound(data) To UBound(data)
       ReturnData(i) = data(i)
        CRC16Lo = CRC16Lo Xor data(i) '每一个数据与CRC寄存器进行异或
        For Flag = 0 To 7
          SaveHi = CRC16Hi
          SaveLo = CRC16Lo
          CRC16Hi = CRC16Hi \ 2            '高位右移一位
          CRC16Lo = CRC16Lo \ 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
            CRC16Lo = CRC16Lo 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
            CRC16Hi = CRC16Hi Xor CH
            CRC16Lo = CRC16Lo Xor CL
          End If
        Next Flag
      Next i
      
      ReturnData(ArraySize + 1) = CRC16Lo             'CRC低位
      ReturnData(ArraySize + 2) = CRC16Hi            'CRC高位
      CRC16 = ReturnData()
    End Function