Thread Subject: Serial input using GUI

It seems that the first time I run my GUI after starting Matlab, I can't get the fscanf to read from the serial object. The timeout happens. But if I simply run the script again and send my data again, the data gets received just fine. It works from then on. Even if I close my GUI and restart it.

My initialization script is:
%----------------------------------------------------
if instrfind ~= NaN; %#ok<FNAN>
  fclose(instrfind);delete(instrfind);
end

s = serial('com1');
s.Terminator = 33;
s.InputBufferSize = 10000;
timeout = 10;
s.Timeout = timeout;
fopen(s);

header = fscanf(s);

header(header==10)=''; % remove the line feeds
nl = find(header==13); % find the carriage returns

if isempty(nl); %if no carriage returns then no more data to be read
    fclose(s); delete(s); clear s;
    
else
% bunch of stuff here to assign received data to workspace.
end
%---------------------------------------------------

I would like to know if anyone can tell me why it runs fine except for the first time I run it after starting Matlab. Also, since this is the first time I have used serial objects, any pointers would be helpful.

Thanks,

Camron

On Nov 9, 4:19 pm, "Camron Call" <camronc...@gmail.cam> wrote:
> It seems that the first time I run my GUI after starting Matlab, I can't get the fscanf to read from the serial object.  The timeout happens.  But if I simply run the script again and send my data again, the data gets received just fine.  It works from then on.  Even if I close my GUI and restart it.
>
> My initialization script is:
> %----------------------------------------------------
> if instrfind ~= NaN;  %#ok<FNAN>
>   fclose(instrfind);delete(instrfind);
> end
>
> s = serial('com1');
> s.Terminator = 33;
> s.InputBufferSize = 10000;
> timeout = 10;
> s.Timeout = timeout;
> fopen(s);
>
> header = fscanf(s);
>
> header(header==10)=''; % remove the line feeds
> nl = find(header==13); % find the carriage returns
>
> if isempty(nl); %if no carriage returns then no more data to be read
>     fclose(s); delete(s); clear s;
>
> else
> % bunch of stuff here to assign received data to workspace.
> end
> %---------------------------------------------------
>
> I would like to know if anyone can tell me why it runs fine except for the first time I run it after starting Matlab.  Also, since this is the first time I have used serial objects, any pointers would be helpful.
>
> Thanks,
>
> Camron

Not sure why it would be doing that.

Does the device you're communicating with have a sleep mode? Perhaps
it's asleep, and the first time you make a call to it, it simply wakes
the device up but doesn't actually sent any recognized commands. Then
once the device is awake, commands are recongnized.

Just a wild guess, but I have a device that does something like that.

The code I included above is inside the callback of a pushbutton in my GUI. Basically it's the download button. Once it's pushed I must actively start the download on the device. Data only flows when I start the upload. I am pretty sure that it's not a problem with the device since it's not really two way communication. All the device does is send. It doesn't even know if something is connected to it.