fscanf over serial port only returns one line at a time...

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Johannes Rebling 2016-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/289167-fscanf-over-serial-port-only-returns-one-line-at-a-time

评论： Walter Roberson 2016-6-10

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I have been trying this for two hours now, so I obviously need help.

I am reading data from the serial port, where a device sends strings of the form:

2.494e-08,0,343

Each string is terminated by a CR/LF which is set as the terminator when setting up the serial protocol. When I read this string using

fscanf(serialObject)

it returns a 17 char string, with the 16th char being the CR char and the 17th being the LR char (13/10).

Now of I read it using a format specifier of the form

fscanf(serialObject,['%f,%i,%i'])

I get the correct results, namely an array containing the numbers 2.494e-08,0,343. So far so good. Unfortunately, fscanf seems to only ever read one line at a time when accessing the serial port, even though thousands of lines are available. So it should return an array with the size 3 x number of lines available.

Any clues on to what I am missing?

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Answer 1

Walter Roberson 2016-6-10

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/289167-fscanf-over-serial-port-only-returns-one-line-at-a-time#answer_225071

http://www.mathworks.com/help/matlab/ref/serial.fscanf.html#zmw57dd0e272866

A read operation with fscanf blocks access to the MATLAB® command line until: * The terminator specified by the Terminator property is read. * The time specified by the Timeout property passes. * The number of values specified by size is read. * The input buffer is filled (unless size is specified)

You have terminators turned on, so the first one encountered will end the fscanf(). If you did not want that you could tell it not to use line terminators -- but if you do that then it is still not going to read indefinitely because it will at most proceed until the input buffer is filled.

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Johannes Rebling 2016-6-10

Thanks a lot for the prompt reply. So I would have to not specify a terminator when setting up the Serial interface? Or is there a way to ignore the terminator when using fscanf?