串口通信重复接收相同数据校验和不同！该如何处理

Option Explicit
    Dim strSj As String

Private Sub Form_Load()
    MSComm1.CommPort = 1
    MSComm1.Settings = "9600,n,8,1"
    MSComm1.InputMode = comInputModeBinary
    MSComm1.RThreshold = 1
    MSComm1.PortOpen = True
End Sub

Private 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 Select
End Sub

------解决方案--------------------

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