Serial - only reads one string.

2013 4 17
1 个回答
回答已采纳
更新时间：2014 7 31
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0 个投票

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

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 采纳的回答

Walter Roberson
Walter Roberson 2013-4-17

0 个投票

You have not configured the line terminator for the serial object.
Also your code
while(while(j<1000)
is invalid syntax.

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Kristoffer
Kristoffer 2013-4-17
编辑：Kristoffer 2013-4-17
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
Walter Roberson 2013-4-17
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
Kristoffer 2013-4-17
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
Walter Roberson 2013-4-17
s1 = serial('COM7', 'Baudrate', 9600, 'Terminator', 'CR/LF');
Kristoffer
Kristoffer 2013-4-18
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
Walter Roberson 2013-4-18
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
siva 2014-7-31
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

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