inconsistent connection to serial port

I am trying to read the current values from a HP-34001A DMM. the code run fine the first time i run it, but if i try to run it again i get the warning:

Warning: The specified amount of data was not returned within the Timeout period for
'readline'.
'serialport' unable to read any data. For more information on possible reasons, see
serialport Read Warnings. 
Failed to read data from the serial port.

If i restart MatLab and restart the DMM the code will run agian 1 time and i again get the error. The DMM also displays 'ERROR'

Here is my code:

function DMM_Collection()
    clc
    clear
    
    % Create the serial port object
    serialPort = '/dev/tty.usbserial-1430'; % Change this to your serial port
    serialObject = serialport(serialPort, 9600);
    
    try
        configureTerminator(serialObject, "LF");
        fopen(serialObject);
    catch fopenError
        fprintf('Error opening serial port: %s\n', fopenError.message);
        return;
    end
    
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Set the instrument in remote mode
    try
        writeline(serialObject, 'SYSTEM:REMOTE');
    catch remoteModeError
        fprintf('Error setting remote mode: %s\n', remoteModeError.message);
        fclose(serialObject);
        return;
    end
    
    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Set the time span and interval for data collection
    stopTime = datetime('now', 'Format', 'yyyy-MM-dd HH:mm:ss.SSS') + seconds(10);
    timeInterval = 0.005;

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Preallocate arrays
    maxIterations = ceil(seconds(stopTime - datetime('now', 'Format', 'yyyy-MM-dd HH:mm:ss.SSS')) / timeInterval);
    time = zeros(1, maxIterations);
    current = zeros(1, maxIterations);

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Collect data
    count = 1;

    while datetime('now', 'Format', 'yyyy-MM-dd HH:mm:ss.SSS') < stopTime
        time(count) = now; 
        writeline(serialObject, 'MEAsure:CURRent:DC?');
        
        % Read data from serial port
        data = readline(serialObject);
        
        % Check if data is read successfully
        if ~isempty(data)
            current(count) = str2double(data); 
            
            % Print timestamp and current
            fprintf('Timestamp: %s, Current: %f\n', datestr(time(count), 'yyyy-MM-dd HH:mm:ss.FFF'), current(count));
            
            count = count + 1;
        else
            fprintf('Failed to read data from the serial port.\n');
        end

        pause(timeInterval);
    end

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Put the instrument in local mode
    try
        writeline(serialObject, 'SYSTEM:LOCAL');
    catch localModeError
        fprintf('Error setting local mode: %s\n', localModeError.message);
    end

    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    % Clean up the serial object
    try
        %fclose(serialObject);
        delete(serialObject);
    catch cleanupError
        fprintf('Error cleaning up serial object: %s\n', cleanupError.message);
    end
end

Answer 1

[Anurag Ojha]

Hello Andres

I found this MATLAB documentation page that provides probable causes and troubleshooting methods of the warning message "Serialport Warning - Unable to Read Any Data". I am adding the documentation link below, I hope this helps you to resolve your query

https://www.mathworks.com/help/releases/R2023b/matlab/import_export/serial-port-warning-unable-to-read-any-data.html