关于MATLAB与串口 通讯的问题

颜扎牧之

Error using serial/fopen (line 72)
Open failed: Port: COM4 is not available. No ports are available.
Use INSTRFIND to determine if other instrument objects are connected to the requested device.

Error in serialTEST>SerialSTART_Callback (line 126)
    fopen(handles.s);

Error in gui_mainfcn (line 96)
        feval(varargin{:});

Error in serialTEST (line 42)
    gui_mainfcn(gui_State, varargin{:});

Error in @(hObject,eventdata)serialTEST('SerialSTART_Callback',hObject,eventdata,guidata(hObject))


Error while evaluating uicontrol Callback


程序运行串口是默认打开的，然后我关闭串口（fclose(handles.s),delete(handles.s),clear handles.s),但再打开的时候会报以上错误，有谁遇到过这种情况么？希望指导一下，不剩感激！