modbus rtu协议可以算是一种事实上的工业标准协议，为许多仪表、PLC等所支持。以前有几个用户问如何使用VB编程来与我们的KND-K3系列PLC通讯，于是整了一个demo程序。这次把这个demo共享，希望能给大家一点帮助。
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 + 1, _
&H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, _ &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, _ &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, _ &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, _ &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, _ &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, _ &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, _ &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, _ &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, _ &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, _ &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, _ &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, _ &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, _ &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, _ &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, _ &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, _ &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, _ &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, _ &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, _ &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, _ &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, _ &H80, &H41, &H0, &HC1, &H81, &H40, &H0, &HC1, &H81, &H40, _ &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, _
&H81, &H40, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40, &H1, &HC0, &H80, &H41, &H1, &HC0, &H80, &H41, &H0, &HC1, &H81, &H40)
End Function
'CRC高位字节值表
Function GetCRCHi(Ind As Long) As Byte
GetCRCHi = Choose(Ind + 1, _
&H0, &HC0, &HC1, &H1, &HC3, &H3, &H2, &HC2, &HC6, &H6, &H7, &HC7, &H5, &HC5, &HC4, &H4, &HCC, &HC, &HD, &HCD, &HF, &HCF, &HCE, &HE, &HA, &HCA, &HCB, &HB, &HC9, &H9, &H8, &HC8, &HD8, &H18, &H19, &HD9, &H1B, &HDB, &HDA, &H1A, &H1E, &HDE, &HDF, &H1F, &HDD, &H1D, &H1C, &HDC, &H14, &HD4, &HD5, &H15, &HD7, &H17, &H16, &HD6, &HD2, &H12, &H13, &HD3, &H11, &HD1, &HD0, &H10, &HF0, &H30, &H31, &HF1, &H33, &HF3, &HF2, &H32, &H36, &HF6, &HF7, &H37, &HF5, &H35, &H34, &HF4, &H3C, &HFC, &HFD, &H3D, &HFF, &H3F, &H3E, &HFE, &HFA, &H3A, &H3B, &HFB, &H39, &HF9, &HF8, &H38, &H28, &HE8, &HE9, &H29, &H
EB, &H2B, &H2A, &HEA, &HEE, &H2E, &H2F, &HEF, &H2D, &HED, &HEC, &H2C, &HE4, &H24, &H25, &HE5, &H27, &HE7, &HE6, &H26, &H22, &HE2, &HE3, &H23, &HE1, &H21, &H20, &HE0, &HA0, &H60, _
&H61, &HA1, &H63, &HA3, &HA2, &H62, &H66, &HA6, &HA7, &H67, &HA5, &H65, &H64, &HA4, &H6C, &HAC, &HAD, &H6D, &HAF, &H6F, &H6E, &HAE, &HAA, &H6A, &H6B, &HAB, &H69, &HA9, &HA8, &H68, &H78, &HB8, &HB9, &H79, &HBB, &H7B, &H7A, &HBA, &HBE, &H7E, &H7F, &HBF, &H7D, &HBD, &HBC, &H7C, &HB4, &H74, &H75, &HB5, &H77, &HB7, &HB6, &H76, &H72, &HB2, &HB3, &H73, &HB1, &H71, &H70, &HB0, &H50, &H90, &H91, &H51, &H93, &H53, &H52, &H92, &H96, &H56, &H57, &H97, &H55, &H95, &H94, &H54, &H9C, &H5C, &H5D, &H9D, &H5F, &H9F, &H9E, &H5E, &H5A, &H9A, &H9B, &H5B, &H99, &H59, &H58, &H98, &H88, &H48, &H49, &H89, &H4B, &H8B, &H8A, &H4A, &H4E, &H8E, &H8F, &H4F, &H8D, &H4D, &H4C, &H8C, &H44, &H84, &H85, &H45, &H87, &H47, &H46, &H86, &H82, &H42, &H43, &H83, &H41, &H81, &H80, &H40)
End Function
2）窗体：FORM1，上面放置的控件如下： Begin VB.Form frmCom Caption = \ ClientHeight = 8235 ClientLeft = 3885 ClientTop = 2250 ClientWidth = 6810 LinkTopic = \ ScaleHeight = 8235 ScaleWidth = 6810
Begin VB.TextBox txtReceive ?注：放置接收上来的IB0数据 Height = 495 Left = 1200 TabIndex = 2 Top = 2280 Width = 1335 End
Begin VB.CommandButton Command1 Caption = \读取IB0\ Height = 495 Left = 2760 TabIndex = 1 Top = 2280 Width = 1695 End
Begin VB.CommandButton cmdSDO
Caption = \置位Q1.1\ Height = 495 Left = 2160 TabIndex = 0 Top = 3720 Width = 1575 End
Begin MSCommLib.MSComm ComK3 Left = 480 Top = 1080 _ExtentX = 1005 _ExtentY = 1005 _Version = 393216 DTREnable = -1 'True End End
① Form_Load事件，在此主要是实现了打开并初始化串口 Private Sub Form_Load()
With ComK3
.CommPort = 1
.Settings = \
.InputMode = comInputModeBinary '二进制收发 .InBufferSize = 512 .OutBufferSize = 512
If (Not .PortOpen) Then .PortOpen = True End With
End Sub
② Form_UnLoad事件，在此主要是关闭串口
Private Sub Form_Unload(Cancel As Integer)
If (ComK3.PortOpen) Then ComK3.PortOpen = False End If
End Sub
③ “置位Q1.1”按钮单击事件
'设置Q1.1为1