VB编写串口通信收不到数据

用vb编写了一个串口通信的程序，但是就是收不到数据请大侠们看看哪里不对
Private Sub Form_Load()
MSComm1.CommPort = 1
MSComm1.Settings = "9600,N,8,1"
MSComm1.PortOpen = True
MSComm1.InputMode = comInputModeBinary
Dim a As Long
End Sub

Private Sub MSComm1_OnComm()
Dim BytesReceived() As Byte
Dim buffer As String
Dim HData As String
Dim i As Integer
Select Case MSComm1.CommEvent
Case comEvReceive '接收十六进制数据。并以十六进制显示
MSComm1.InputLen = 0
buffer = MSComm1.Input '接收数据至字符串中
BytesReceived() = buffer '将数据转入Byte数组中
For i = 0 To UBound(BytesReceived) '显示结果以十六进制显示
If Len(Hex(BytesReceived(i))) = 1 Then
HData = HData & "0" & Hex(BytesReceived(i))
Else
HData = HData & Hex(BytesReceived(i))
End If
Text1.Text = HData
'最后将结果后入Text1中
MSComm1.OutBufferCount = 0 '清除发送缓冲区
MSComm1.InBufferCount = 0 '清除接收缓冲区
Next
End Select
End Sub

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