How to close serial port in R2019b

Good morning,

I am porting my code to the new serialport() interface, but I have been unable to find how to close the serial port once I have finished reading from it.

What is the function to do that in R2019b?

Thanks,

Javier.

Answer 1

[Walter Roberson]

The new serialport() interface does not use fopen() or fclose() . You just delete the object to close it.

I prefer the fopen() / fclose() interface myself... but then I used to write modem control programs where it was common to want to configure a port and open and close it while not deleting it.

[Will Reeves]

Hi, thanks for the reply however this doesn't work for my situation in regard to storing serial port objects within a structures or classes.

For example:

a=serialport('COM3',9600,'Timeout',5);
clear('a')
a=serialport('COM3',9600,'Timeout',5);

works fine, however this doesn't:

a.serialPortObject = serialport('COM3',9600,'Timeout',5);
rmfield(a,'serialPortObject')
a.serialPortObject = serialport('COM3',9600,'Timeout',5);

This is a real issue for me since I create classes to control our serial port devices and at the moment I don't have a way of detecting and/or cleanly destroying previous serial port objects that remain connected.

Perhaps is an issue for rmfield? I'd assumed that removing a field deleted it from memory... clearly not cleanly!

Any advice?

[Walter Roberson]

For the purpose of debugging, it would be interesting to

instrfind('Type', 'serial')

and see what comes out.

[Will Reeves]

Thanks, I tried this and the anwer is empty, [].

[Will Reeves]

Support said the way to delete a serialport field in a structure is to run delete(a.serialPortObject). This does work (but not remove the field!) but my issue is that I have the port defined in a class. for instance:

  classdef aSerialPortControllingClass
    properties
        port='COM3';    % communications port address
        interfaceObj    % communications port
        
    end
    
    methods
        function obj = chough(varargin)
            % CHOUGH Construct an instance of this class
            
            % get the port if not standard
            if length(varargin)==1
                obj.port=upper(varargin{1});
            end
            
            % create serial port instance
            obj.interfaceObj = serialport(obj.port,9600,'Timeout',5);
            
        end
        
        function delete(obj)
            % cleanly delete the serial port object!
            delete(obj.interfaceObj);
        end
    end
  end

if I run

  a=aSerialPortControllingClass;

If I delete "a" everything is fine and I can recreate it no problem.

What I can't do is call

  a=aSerialPortControllingClass;
  a=aSerialPortControllingClass;

Because I can't seem to handle the existence of a pre-existing connection to a serialport.

It was easy with "serial" and "instrfind" - but instrfind finds nothing!

Am I just being really dense?!!

[Walter Roberson]

Use Static Data ? https://www.mathworks.com/help/matlab/matlab_oop/static-data.html#buvywj1

[Will Reeves]

Thanks, without spending a bit of time working out how to do do this I hacked it using a global variable:

% create serial port instance
            global interfaceObj
            
            interfaceObj=serialport(obj.port,9600,'Timeout',5);

then in the "delete" function:

        function delete(obj)
            % cleanly delete the serial port object!
            global interfaceObj
            delete(interfaceObj);
        end

Feels dirty, but works as I want it to. the instance of the class can be initiated multiple times and the serial port can be created without issues. Seems as if there is some missing matlab functionality around the "serialport" command?

[Pedro Inácio]

Thanks Walter and Javier for yours feedback. Indeed I'm having the same troubles to solve serialport, it is a nightmare. I couldn't imagine Matlab will ever launch new functions with so few and poor documentation for serialport and such bad handling of the serial objects.

As Walter suggested, so far the unique method I've also found to terminate the serialport connection requires to have access to the serial object and than delete the object:

interfaceObj.delete;

After delete the object we can verify the connection was closed, which implies Matlab has internaly handled the connection, therefore somehow it is possible to terminate the connection but not available in documented user interface. Also, after delete the object, It requires to re-call the serialport to start a new connection... It is boring and anoying!

If an unexpected error occurs, only through the use of a try-catch statement is possible to relatively avoid crashing the Matlab, which, in cases of real time measurements it means human presence is required to handle and restart a script or app! It is a completely a nightmare. I think this is the major issue with serialport.

It is missing the close / disconnect function, as well a method to recover the handle created with serialport, which pretty easy to handle with fopen/fclose interface, as refered before by Walter.

[Walter Roberson]

/Applications/MATLAB_R2021a.app/toolbox/matlab/serialport/+internal/Serialport.m handles delete() by clearing a stored InstrumentImpl object. Presumably the delete() method of InstrumentImpl takes care of the details of disconnecting the object. However the details are inside /Applications/MATLAB_R2021a.app/toolbox/shared/instrument/+instrument/+internal/InstrumentImpl.p which we cannot read.

The stored InstrumentImpl property is inside

   properties (Hidden, Access = ...
            {?internal.Serialport, ?instrument.internal.ITestable})

so you cannot get at the object. Not unless perhaps struct()

[Will Reeves]

within a class with a serialport assigned to a property,

delete(obj.serialPortInstance)

doesn't seem to work for me. Could you let me know the correct syntax for clean deletion from within a class?

obj.serialPortInstance=[];

doesn't work for me either...

Thanks!

Answer 2

[Michael Borovik]

Create the object with comport and baudrate. This will open the port.

a = serialport(comport,baudrate);

Write an empty matrix to clear the port. This will close the port and let other processes to access it (Arduino IDE for that matter). This will work where "clear a" would not. For example a handle class that keeps "a" as one of the properties.

a = [];

[James]

Thanks Michael ~ that works for me !

I'm new to Matlab. Writing [ ] to the port object isn't exactly intuitive (to me anyway).

Answer 3

[JAVIER BURGUES CALDERON]

Thanks Walter. I agree that the fopen/fclose interface was more intuitive.

Do you know if it is possible to delete a callback function currently associated to a serialport object, without deleting the object?

Thanks,

Javier.

[Sakari Vekki]

Late to the party but this should work:

configureCallback(serialhandle, "off");

where serialhandle is your serialport object.

[Walter Roberson]

Thanks, Sakari Vekki, I had not noticed that method before.