求问:关于用西门子TC35发短信

' 设置模块短信到来提示
Private Function SetSmsTip() As Boolean
   On Error GoTo ErrDisp
   Dim s As String, sTim As Date
   
   sTim = Now()
   With comSms
       .InBufferCount = 0
       .Output = "AT+CNMI=1,1,0,0,1" + vbCrLf
       Do
           DoEvents
           s = s + comSms.Input
      ??????S怎么有时候总是接收不到,有时候就可以??为什么?????
       Loop Until (InStr(s, "OK") > 0 Or DateDiff("S", sTim, Now()) > 1)
   End With
   SetSmsTip = (InStr(s, "OK") > 0)

   Exit Function
ErrDisp:
   mError.WriteErrorLog "frmSms.SetSmsTip", err.number & " " & err.Description
   
End Function