Matlab GUI: Reading from Serial port and showing in different listboxes at the same time

I am working with serial port and multiple list boxes to read data in serial port. The listboxes are used to read specific data (suppose the data is coming from 3 different sources, so I have 3 listboxes).

Now the problem:

I want to read all the data separately and continuously. I mean, when I am clicking one listbox (e.g. listbox#2) after reading listbox#1's data, the listbox#1 automatically stops, so again I need to click listbox#1 to read the data for listbox#1. But I want to get the data continuously in all the listboxes without clicking (clicking for first time to initializing) every time. How can I achieve this? I have tried timer function but it shows following error: Error while evaluating TimerFcn for timer 'timer-1'.

Sample code:

 function main_OpeningFcn(hObject, eventdata, handles, varargin)
 handles.output = hObject;
 handles.timer   = timer(...
 'ExecutionMode', 'fixedRate', ...       % Run timer repeatedly
 'Period', 1, ...                        % Initial period is 1 sec.
 'TimerFcn', {@listbox1_Callback, handles});
 guidata(hObject, handles);

     function listbox1_Callback(hObject, eventdata, handles)
     %serConn is the connection to COM port
     out = fscanf(handles.serConn);
     string = 'degrees1';
     t=1;
     while(t < 15)
     if strncmp(out,string,8)
     rxtext = out(14:15);
     currList = get(handles.listbox, 'String');
     set(handles.listbox,'String',...
       [currList ;  [temp]]);
     end
     pause(5);
     t = t+1;
     end
     end