Hi Chi,
The error message indicates that the fread operation was not completed before the timeout.
You could go about fixing the issue in these two ways I can think of.
1) Specify the size of the data you want to read, fread(serial_obj,size). If you do not specify the size, it is going to try to read the data equal to the entire InputBufferSize, which is 512 bytes by default, and if that much data is not available it won't terminate the read and timeout is reached. You can refer to this documentation to learn how to specify the size of data to read and to set the InputBufferSize for the serial object, https://www.mathworks.com/help/matlab/ref/serial.fread.html?s_tid=doc_ta#f102-512480
2) Another approach you can take if you do not know the size of the data to be read is to read the data asynchronously. Here an example of how you can do it:
%Callback function to read data once a speficied chunck of data is
%available to read
function myCallbackFcn(obj, event)
data = fread(obj, obj.BytesAvailable, 'uint8');
end
clear all; close all;
s = serial('COM7', 'BaudRate', baudrate, 'InputBufferSize', 2000); % Set a large enough input buffer size
set(s, 'BytesAvailableFcnMode', 'byte');
set(s, 'BytesAvailableFcnCount', 1024); % Callback function will be triggered everytime this much data is available to read
set(s, 'BytesAvailableFcn', @myCallbackFcn); % Set the callback function
fopen(s);
Refer to this documentation if you would like to learn more about the serial object, https://www.mathworks.com/help/matlab/ref/serial-properties.html
