Serial - only reads one string.

Hi

I have a microcontroller with a sensor. The uC sends out a string every tenth of a second to the COM-port. The string is filled with data XXX (Where XXX is 000-999)

Looks like this:

                          char output_verbose[] = {"XXX\r\n"};

The matlab-code is like this:

s1=serial('COM7','Baudrate',9600);
fopen(s1);
value=0;
str='';
sen=0;
j=1;

 while(j<1000)
      str=fscanf(s1);
      sen=str2num(str);
      accX(j)=sen;
      plot(j,value);
      drawnow;
      j=j+1;
  end;

fclose(s1);
delete(s1);
clear s1;

The probem after i have debugged a bit, is that when i want to read value number 2, the string is empty. It wont get the string from the COM-port again. And the uC sends the values 10 times a second, this is checked via PuTTY. I also have a LED that blinks everytime it sends.

Please help me

Answer 1

[Walter Roberson]

You have not configured the line terminator for the serial object.

Also your code

while(while(j<1000)

is invalid syntax.

[Kristoffer]

That is true. I was copying part by part into the forum. So in the real code, it is not like that.

But i found out that I have to close and open the serial-port for each input. And now it samples. Here is the code, if it can help some others.

Tips for doing the code better is welcome

s1=serial('COM7','Baudrate',9600);
accX=0;
str='';
sen=0;
j=1;
x=0;

while(j<300)
    fopen(s1);
    str=fscanf(s1);
  fclose(s1);
    sen=str2num(str);
    accX(j)=sen;
    plot(accX);
  axis([(-50+j) (5+j) 0 1000]);
    drawnow;
    j=j+1;

end;

fclose(s1);
delete(s1);
clear s1;

[Walter Roberson]

You definitely should not need to close and open the port. But you do need to set the termination character. See http://www.mathworks.com/help/instrument/terminator.html

[Kristoffer]

How do I do that in MATLAB? Every string ends with \r\n from the uC, I would think I can use that as a terminator?

[Walter Roberson]

s1 = serial('COM7', 'Baudrate', 9600, 'Terminator', 'CR/LF');

[Kristoffer]

Thank you for your help Walter. Now it runs much better. I could not use CR/LF as terminator for some reason, so I used 000.

 char output_verbose[] = {"XXX 000 \r\n"};

s1 = serial('COM7', 'Baudrate', 9600, 'Terminator', 000 );
fopen(s1);
accX=0;
str='';
sen=0;
j=1;
x=0;

while(j<3000)
    str=fscanf(s1);
    sen=str2num(str);
    accX(j)=sen/100;
    plot(accX);
  axis([(-50+j) (5+j) 0 10]);
    drawnow;
    j=j+1;

end;

fclose(s1);
delete(s1);
clear s1;

[Walter Roberson]

Note: in C, "XXX 000 \r\n" the 000 part is '0' '0' '0', but when you use 'Terminator', 000 in MATLAB, that is the same as 'Terminator', 0 -- a binary 0; in C that would be coded as \0, "XXX \0\r\n"

[siva]

hi i also tried the same to interface uc with matlab but the terminator error persists even after i made the above changes coudl u clarify this please