* mscom为什么只响应两次后OnComm事件没有反应

*求助* mscom为什么只响应两次后OnComm事件没有反应？
程序在进入MSCOMM ONCOMM事件后；响应了两次，就没反应了。请教各位大虾：

VB code

Private Sub ChangeMScom(ChgCom As Integer)'改变MSCOM设置        Select Case ChgCom                              Case 0                                 MSComDL.CommPort = "9"                                          MSComDL.RThreshold = 1                     MSComDL.InputMode = comInputModeBinary                     MSComDL.Settings = "9600,m,8,1"                     MSComDL.PortOpen = True                                     Case 1                                         MSComDL.PortOpen = False                                     MSComDL.CommPort = "9"                                          MSComDL.RThreshold = 1                     MSComDL.InputMode = comInputModeBinary                     MSComDL.Settings = "9600,m,8,1"                     MSComDL.PortOpen = True                                                Case 2                                     MSComDL.CommPort = "9"                                          MSComDL.RThreshold = 1                     MSComDL.InputMode = comInputModeBinary                     MSComDL.Settings = "9600,s,8,1"                     MSComDL.PortOpen = True                                                Case 3                                     MSComDL.PortOpen = False                                     MSComDL.CommPort = "9"                                          MSComDL.RThreshold = 1                     MSComDL.InputMode = comInputModeBinary                     MSComDL.Settings = "9600,s,8,1"                     MSComDL.PortOpen = True                                                Case Else                                     MSComDL.PortOpen = False                                     MSComDL.CommPort = "9"                                          MSComDL.RThreshold = 1                     MSComDL.InputMode = comInputModeBinary                     MSComDL.Settings = "9600,m,8,1"                     MSComDL.PortOpen = True                                        End Select                        End SubPrivate Sub DownPro_Click() '开始                           Dim ProDLArr() As Byte                                          ReDim ProDLArr(0) As Byte                                          WSUDConFlag = 0                                                                                                     WSUDFlag = 50                                           ChangeMScom (0)                                          Call TimeDelay(50, "") '延迟50MS                                          ProDLArr(0) = 1                                           MSComDL.Output = ProDLArr                                          End Sub