Serial Port opening problem

I'm trying to acquire values from a microcontroller using the serial port. However, I'm facing a strange bug!

when I try to run the program for the first time it works and when I try to run it again it gives me an error saying that cannot open the port! But if I close matlab and open it again and run the program it works for the first time only and then same problem arises!

Can anyone help me please ?

Thanks in advance

[Walter Roberson]

Are you closing the port after use?

[Abdel Rahman Bekawi]

I'm using try and catch and in the catch I'm closing the port

[Ruger28]

Without seeing your code, it seems like what Walter is getting at is that you are not closing it after you are done, and on the next iteration you are trying to open it up while it is open already. Try closing it when you are done.

[Abdel Rahman Bekawi]

I will try then to remove try and catch and close after my code is done and see!

thanks a lot for your help

[Abdel Rahman Bekawi]

Here is the code from the tutorial I'm following in this link https://os.mbed.com/cookbook/Interfacing-with-Matlab

function accell()
 
TIMEOUT = 5;    %time to wait for data before aborting
XPOINTS = 50;   %number of points along x axis
 
try
    %create serial object to represent connection to mbed
    mbed = serial('COM4', ...
                  'BaudRate', 9600, ...
                  'Parity', 'none', ...
                  'DataBits', 8, ...
                  'StopBits', 1);       %change depending on mbed configuration
    
    set(mbed,'Timeout',TIMEOUT);        %adjust timeout to ensure fast response when mbed disconnected
    
    fopen(mbed);        %open serial connection
 
    position = 1;       %initialise graph variables
    time = 1;
    x = [(1:XPOINTS)' (1:XPOINTS)' (1:XPOINTS)'];
    xlabels = (1:XPOINTS);
    y = zeros(XPOINTS,3);
    % in my CASE I'm NOT having the CONDITION to be alwase TRUE as in here
    while (1)       %loop forever (or until an error occurs)
        
        values = fscanf(mbed, '%f,%f,%f');    %get values into vector
                                              %assumes data formatted as
                                              %'1,2,3'
        y(position,:) = values';    %put into y to be displayed
        
        %update position on x-axis and x-axis labels
        xlabels(position) = time;
        time = time + 1;
        if (position < XPOINTS)
            position = position + 1;
        else
            position = 1;
        end
 
        %display
        plot(x,y);
        set(gca, 'XTick', 1:XPOINTS);
        set(gca, 'XTickLabel', xlabels);
 
        drawnow;    %this is required to force the display to update before the function terminates
    end
 
    fclose(mbed);   %close connection (this should never be reached when using while(1), but included for completeness)
    
catch
    %in case of error or mbed being disconnected
    disp('Failed!');
    fclose(mbed);   %close connection to prevent COM port being lokced open
end 

Answer 1

[Murugan C]

Hi

you should check, how many ports are open and closed using instrfind syntax in matlab.

>> instrfind

   Instrument Object Array

   Index:    Type:     Status:   Name:  
   1         serial    closed    Serial-COM4
   2         serial    closed    Serial-COM4
   3         serial    closed    Serial-COM1
   4         serial    closed    Serial-COM1
   5         serial    closed    Serial-COM1
   6         serial    closed    Serial-COM1
   7         serial    open      Serial-COM1

now, easily we can close all ports using fclose. and should delete that object.

   fclose(instrfind)
   delete(mbed)

correct your as like below..

try
    mbed = serial('COM1', ...
                  'BaudRate', 9600, ...
                  'Parity', 'none', ...
                  'DataBits', 8, ...
                  'StopBits', 1);       %change depending on mbed configuration
    .......
catch
    %in case of error or mbed being disconnected
    disp('Failed!');
    fclose(mbed); 
    fclose(instrfind);
    delete(mbed);
end

[Abdel Rahman Bekawi]

Thanks Murugan and everyone for the help it worked out!