Problems with fscanf using serial

Dear Community

I have a microcontroller which is connected to my PC via a serial port. Thereby I have some problems by reading the incoming data. Using HTerm it is possible to get the correct data in Ascii format from the microcontroller (see figure below). Only the last line ([006C221C249C24C42A]), which contaisn the sensor data, is of interrest.

Here you can see my code:

 %Set Parameter
 s = serial('COM4');
 set(s, 'BaudRate', 115200, 'DataBits', 8, 'StopBits',1, 'Terminator', ...
    'CR/LF', 'ByteOrder', 'bigEndian', 'Parity', 'none');

 %Communication begin
 fopen(s);

 % record file for debugging
 s.RecordName = 'myRecord.txt';
 record(s);

 %%set up MCU

 % start MCU
 fprintf(s, startMCU);

 % set High Data Rate
 fprintf(s, setHighDataRate);

 fprintf(s, agcTtoggle);

 fprintf(s, ampmToggle);

 % convert to 8 byte mode for sampling sensors
 fprintf(s, convertTo8ByteMode);

 %%end set up MCU

 % set up and sample
 fprintf(s, setUpAllSensors);
 fprintf(s, sampleAllSensors);
 fprintf(s, readingBlock0x00);

 % delay to sample
 pause(0.5);
 fprintf(s, readingBlock0x09);

 condition = true;
 count = 0;
 while condition
    received = upper(fscanf(s));
    if strcmp(received, 'REQUEST MODE.');
        count = count+1;
    end
    if count == 3
        condition = false;
    end   
 end % while condition

 data = fscanf(s);

 fclose(s);
 delete(s);
 %Communication end

 % delete serial port for further communication
 delete(instrfindall)

Matlab gives out a warning after a couple of seconds: "Warning: Unsuccessful read: A timeout occurred before the Terminator was reached.. "

Then when I break the communication manually it displays the error: "Error using serial/fscanf (line 154)

Unsuccessful read: Error using serial/fscanf (line 154)"

Has somebody an idea how I can fix that? Thank for your help

Best regards

Klaus

Answer 1

[Klaus Schürch]

It works now. I did not know that the function "fscanf()" adds a terminator to my transmissions. Now I am using "fwrite()" which does not send an additional terminator.

[Walter Roberson]

fscanf() does not add a terminator, fscanf() by default reads up to and including the terminator that is already there in the buffer.

fprintf() does add a terminator to output if you do not specify a format string, but leaves out the terminator if you specify a format string.

fprintf(s, 'hello')

would be the same as

fprintf(s, '%s\n', 'hello')

which would add the line terminator. But

fprintf(s, '%s', 'hello')

would not add the line terminator.

fwrite(s, 'hello')

is not going to add the line terminator.

Answer 2

[Walter Roberson]

fscanf() is probably including the CR/LF as part of the returned text. You then compare for exactly 'REQUEST MODE.' not for the later being a leading prefix of the line.

I suggest you switch to fgetl(s) from fscanf(s) as fgetl() is defined to remove line terminators.

[Klaus Schürch]

Thank's for your help. I can read the first three lines with fgetl(s), up to " ISO15693: [5D0E000000A207E0,5B]TRF7970A EVM \r\n". When I send the next commant to the microcontroller MATLAB displays: "Warning: Unexpected Warning: A timeout occurred before the Terminator was reached." Thereby the received variable is empty, which I suggest comes from line 4 (\r\n\r\n). Then I do not get any further messages. Is it possible that the timeout is too small? My controller sends a message every 0.5 seconds.