Function CreateSerPort(PortName as String) as Integer  ' Return 'handle' to port.
  ' Where PortName is like "Com1", "Com2", ...
  
  Declare Function CreateFile LIB "kernel32" Alias "CreateFileA" _
       (FName as CString, DesAccs as Integer, Share as Integer, _
        SecAttr as INTEGER, CreateDisp as Integer, Flags as Integer, _
        Template as Integer) as Integer
  
  Dim LocHandle as Integer
  Dim GEN_READ as INTEGER   = &h80000000
  DIM GEN_WRITE as INTEGER  = &h40000000
  DIM EXISTING as INTEGER   = 3
  DIM OVERLAPPED AS INTEGER = &h40000000
  DIM INVALID_HANDLE as INTEGER = -1
  
  DIM RetVal as INTEGER
  
  LocHandle = CreateFile(PortName, GEN_READ + GEN_WRITE, _
                          0, 0, EXISTING, OVERLAPPED, 0)
  
  'Note it auto-converts 'String' to CString on the fly
  
  IF LocHandle = INVALID_HANDLE THEN
    ' Is bad port, abort.
    RETURN INVALID_HANDLE
  END IF
  
  Return LocHandle

END FUNCTION

Sub ClearDTR(PortHandle as INTEGER)
  ChangePort(PortHandle, 6)
END SUB

Sub ChangePort(PortHandle as INTEGER, Cmd as INTEGER)

  Declare Function EscapeCommFunction LIB "kernel32" _
      ( SerHandle as INTEGER, SerFunc as Integer) as INTEGER
  ' Function command values...
  ' SETXOFF==1, SETXON==2, SETRTS==3, CLRRTS==4, SETDTR==5, CLRDTR==6
  ' RESETDEV==7, SETBREAK==8, CLRBREAK==9
  ' 
  ' Set RTS HIGH, wait, then Set it LOW
  Dim RetVal as INTEGER
  RetVal = EscapeCommFunction(PortHandle, Cmd)

END SUB
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