Reading data only when present - matlab

Question

I'm trying to read the data from the COM3 port.
I'm using this code:
in = fscanf(s);
if(in == 'A')
fclose(s);
break;
end
The problem is that when no data is sent to the com3 port, the fscanf() will wait for a certain time interval and then give a timeout.
Is there a way to read data only when it is present?

Answer 1

Read only when data present
You can read out the BytesAvailable-property of the serial object s to know how many bytes are in the buffer ready to be read:
bytes = get(s,'BytesAvailable'); % using getter-function
bytes = s.BytesAvailable; % using object-oriented-addressing
Then you can check the value of bytes to match your criteria. Assuming a char is 1 byte, then you can check for this easily before reading the buffer.
if (bytes >= 1)
in = fscanf(s);
% do the handling of 'in' here
end
Minimize the time to wait
You can manually set the Timeout-property of the serial object s to a lower value to continue execution earlier as the default timeout.
set(s,'Timeout',1); % sets timeout to 1 second (default is 10 seconds)
Most likely you will get the following warning:
Unsuccessful read: A timeout occurred before the Terminator was
reached..
It can be suppressed by executing the following command before fscanf.
warning('off','MATLAB:serial:fscanf:unsuccessfulRead');
Here is an example:
s = serial('COM3');
set(s,'Timeout',1); % sets timeout to 1 second (default is 10 seconds)
fopen(s);
warning('off','MATLAB:serial:fscanf:unsuccessfulRead');
in = fscanf(s);
warning('on','MATLAB:serial:fscanf:unsuccessfulRead');
if(in == 'A')
fclose(s);
break;
end