How can I send data to the same COM port from different functions without having to constantly open the comport?

Hi I wanted to know how I can pass data to a COM port from different callbacks without constantly having to open a COM port in the different callbacks?

so here is the code

function submitButton_Callback(hObject, eventdata, handles)
% hObject    handle to submitButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
if(get(handles.HitButton,'Value') == 1)
    filename = 'testing.xls';
    writevar({'Hit'},1,filename);
    set(handles.text2,'visible','off');
    set(handles.words,'visible','off');
    set(handles.rating,'visible','on');
    set(handles.readyToGo,'visible','off');
    set(handles.readyButton,'visible','off');
    set(handles.submitButton,'visible','off');
    set(handles.rateButton, 'visible','on');
    set(handles.HowSure,'visible', 'on');
    drawnow;
    sPort=serial('COM4');
    fopen(sPort);
    fprintf(sPort, '%d', 3);
    fclose(sPort);
    delete(sPort);
else
    filename = 'testing.xls';
    writevar({'Bit'},1,filename);
    set(handles.text2,'visible','off');
    set(handles.words,'visible','off');
    set(handles.rating,'visible','on');
    set(handles.readyToGo,'visible','off');
    set(handles.readyButton,'visible','off');
    set(handles.submitButton,'visible','off');
    set(handles.rateButton, 'visible','on');
    set(handles.HowSure,'visible', 'on');
    drawnow;
    sPort=serial('COM4');
    fopen(sPort);
    fprintf(sPort, '%d', 3);
    fclose(sPort);
    delete(sPort);

end

function readyButton_Callback(hObject, eventdata, handles)
% hObject    handle to readyButton (see GCBO)
% eventdata  reserved - to be defined in a future version of MATLAB
% handles    structure with handles and user data (see GUIDATA)
s = load('train.mat');
sPort=serial('COM4');
fopen(sPort);
fprintf(sPort, '%d', 1);
player = audioplayer(s.y,8192);
playblocking(player);
fprintf(sPort, '%d', 2);
fclose(sPort);
delete(sPort);
%pause(4);
set(handles.text2,'visible','on');
set(handles.words,'visible','on');
set(handles.HowSure,'visible', 'off');
set(handles.rating,'visible','off');
set(handles.readyToGo,'visible','off');
set(handles.readyButton,'visible','off');
set(handles.submitButton,'visible','on');

drawnow;

as you can see I have to open the Com port for each function. Ideally I would like it to remain open and be accessible

Answer 1

[Geoff Hayes]

Yasir - try saving your serial port object to the handles structure so that the other callback will be able to access it. For example, in either of the callbacks do

 if ~isfield(handles,'serialObj')
     handles.serialObj = serial('COM4');
     fopen(handles.serialObj);
     guidata(hObject,handles);
 end

 fprintf(handles.serialObj,...);

In the above, we check to see if the serialObj is a field of the handles structure. If it isn't, then we create and open it. We use guidata to save the updated handles structure so that the other callbacks (when fired) receive this updated structure with the open serial object.