串口通信重复接收相同数据校验和不同！该如何处理

串口通信重复接收相同数据校验和不同！
Private Sub MSComm1_OnComm()
  Dim intInputLen As Integer
  Dim str as string
  Select Case MSComm1.CommEvent
  Case comEvReceive
  MSComm1.InputMode = comInputModeBinary
  intInputLen = MSComm1.InBufferCount
  ReDim bytInput(intInputLen)
  bytInput = MSComm1.Input
  jieshou
  End Select
  Dim i As Integer
  Dim decSum As Integer, hexSum As String
  For i = 1 To Len(str) - 2 Step 2
  decSum = decSum + ("&H" & Mid(str, i, 2))
  Next
  decSum = decSum And 255
  hexSum = Hex(decSum)

If hexSum = Mid(str, 17, 2) Then 
MsgBox "正确!", vbInformation, "提示"
else
MsgBox "错误!", vbInformation, "提示"
End if
Public Function jieshou()
  Dim i As Integer
  For i = 0 To UBound(bytInput)
  str = str & Right("0" & Hex(bytInput(i)), 2)
  Next
end function
16进制发送 aa5500123456780013 
第一次提示正确 第二次发提示错误
我让text1.text=mid(str,17,2)
发现第一次发是13 发完第一次发第二次是39要添加些什么呀！谢了！

[解决办法]

VB code

Option Explicit    Dim strSj As StringPrivate Sub Form_Load()    MSComm1.CommPort = 1    MSComm1.Settings = "9600,n,8,1"    MSComm1.InputMode = comInputModeBinary    MSComm1.RThreshold = 1    MSComm1.PortOpen = TrueEnd SubPrivate Sub MSComm1_OnComm()    Dim bytInput() As Byte    Dim intInputLen As Integer    Dim str As String    Select Case MSComm1.CommEvent        Case comEvReceive            MSComm1.InputMode = comInputModeBinary            intInputLen = MSComm1.InBufferCount            ReDim bytInput(intInputLen)            bytInput = MSComm1.Input            Dim i As Integer            For i = 0 To UBound(bytInput)                strSj = strSj & Right("0" & Hex(bytInput(i)), 2)            Next            If Mid(strSj, 1, 2) = "AA" And Len(strSj) = 18 Then                Dim decSum As Integer                Dim hexSum As String                For i = 1 To Len(strSj) - 2 Step 2                    decSum = decSum + ("&H" & Mid(strSj, i, 2))                Next                decSum = decSum And 255                hexSum = Hex(decSum)                If hexSum = Mid(strSj, 17, 2) Then                    Label1.Caption = "正确!"                Else                    Label1.Caption = "错误!"                End If                strSj = ""            End If    End SelectEnd Sub
[解决办法]
变量定义要养成好习惯，要习惯使用Option Explicit强制定义变量

你要明白的是在你定义全局变量str前，MSComm1_OnComm()中的str并不是jieshou()里的str

1、定义全局变量str
2、删除MSComm1_OnComm()中的dim str as string
--------------------

Dim str As String

Private Sub MSComm1_OnComm()
 Dim intInputLen As Integer
 Select Case MSComm1.CommEvent
 Case comEvReceive
 MSComm1.InputMode = comInputModeBinary '这句应该放在mscomm初始化里
 intInputLen = MSComm1.InBufferCount
 ReDim bytInput(intInputLen)
 bytInput = MSComm1.Input
 jieshou
 End Select
 Dim i As Integer
 Dim decSum As Integer, hexSum As String
 For i = 1 To Len(str) - 2 Step 2
 decSum = decSum + ("&H" & Mid(str, i, 2))
 Next
 decSum = decSum And 255
 hexSum = Hex(decSum)

If hexSum = Mid(str, 17, 2) Then
MsgBox "正确!", vbInformation, "提示"
Else
MsgBox "错误!", vbInformation, "提示"
End If

str = ""

End Sub

Public Function jieshou()
 Dim i As Integer
 For i = 0 To UBound(bytInput)
 str = str & Right("0" & Hex(bytInput(i)), 2)
 Next
End Function