fprintf, the option '%6.4f'', RS232, and ascii Code ( Explanation and help pleas)

So, It's been 2 month now that I try to send an ascii order to a motor without any succesfull code. But today, I succed to send a stop message to the motor this way :

fprintf(s, '%6.4f','A2')

And it recognise other order, for example, if I send A1 (start engine) it works, if I send A30020 that is for "go to speed 20 km/h" it change the speed, but not in a good way at all, emergency stop used in that case !!!!

So first, can you explain to me this option '%6.4f', I have found example, but no explanation on it And secondly, do you understand why for sending 'A2' it works. If you want more information of the order in ascii I have to send, follow this link, it's the Trackmaster Protocol for treadmill.

http://pdfcast.org/pdf/qsdqsddd

Best regards.

Stanislas A

[Cedric]

Look at Jan's answer, and evaluate

 >> fprintf('%6.4f', 'A30020')

what you get on stdout (the output in the command window) is what you are sending on your port. You might want to either understand the formatSpec, or to use a lower level I/O function. For that, look at what is available here: http://www.mathworks.com/help/matlab/serial-port-devices.html

[Stan sdsd]

Thank you Cedrid Wannaz for your answer, I am cheking on it. For the low level, I tried to use the fwrite. But I have ascii code, and it doesn't work. I tried fwrite(s, 'A2') and it doesn't stop the motor :( best regards Stanislas

[Cedric]

I think that there is a basic misunderstanding somewhere, because all these conversions that you are mentioning in the comments below are way too complicated.. in the sense that people who developed your device at Siemens probably went for simplicity in the protocol.

To me, that commands look like HEX doesn't change the fact that everything has to be sent in ASCII. What I don't get from the document is whether there is a terminator or not.

Have you tried to execute the following, as mentioned below?:

 fprintf(s, '%s', 'A0') ;
 fprintf(s, '%s', 'A40500') ;
 pause(2) ;
 fprintf(s, '%s', 'A40000') ;
 pause(2) ;
 fprintf(s, '%s', 'A4-0250') ;
 pause(4) ;
 fprintf(s, '%s', 'AA') ;

.. maybe commenting out the first line.

[Jan]

ASCII communication is not really usual. I still can imagine, that the device communicates with simple bytes, which are explained in HEX format.

[Stan sdsd]

@Cedrid Wannaz : I can't try it today, you will have an answer tomorrow, I will try your code, and give you the fscanf answers. For the terminator, they said to me that it doesn't matter... :(

Answer 1

[Jan]

The documentation of your device say, that you need:

"A3" plus 4 octects.

Why do you assume that fprintf(s, '%6.4f', 'A30020') does this job?

[EDITED]

The linked documentation says:

 "A3" and 4 octets

Actually "A3" looks like a hexdecimal values, such that e.g. this could be sufficient:

fwrite(s, sscanf('%x', 'A3'), 'uint8');

or

fwrite(s, sscanf('%2x', 'A30020'), 'uint8');

(or do we need '%.2x'? Please try this by your own). But this is a pure guess and most likely this will get more clear, when you explain why you have chosen fprintf and '&6.4f'.

[Stan sdsd]

Yes A3 + 4 octet : for 20 km/h you have to write 0200, for 2 km/h, it's 0020. For 2.2 Km/h it's 0022. Well I think, that what the pdf say. But What I don't understand, is why sending fprintf(s,'%s','A2') [A2 is for stopping the motor] doesn't work. And fprint(s,'%6.4f', 'A2') does work fine ! Apparently, sending fprintf(s, '%6.4f', 'A30020') is understand as a speed command, like in the pdf, but the speed is not correct, so yes I will check on your question. But if you have the answer of my previous question : why does '%6.4f' make it work, it will be awesome. Maybe I have to send more precis code, like %1.2f or something else. I don't know the fprintf option, I discovered it in a forum, I try for fun, because I don't succeed to send my ascii code with other code : %s, %c with hex2dec, or uin8 etc... Sorry for my bad english, I am a french student, and still young. Best regard Jan Simon, And thank you for your help in this matter. Stanislas

[Stan sdsd]

For your update : I will try it on monday, tomorw I have some meeting. And I will put back here the results precisely. Comment : on the documentation, you can read that all the numbers are send in ascii. And that's where I am lost. Does A2 or A1 or A3 are ascii, and need to be send that way, or do I have to convert them ?

[Stan sdsd]

Okay, here are the news. First, and it's very important, the code in the documentation are in HEX !!!! Not ASCII, But I need to send them to the microcheap in ascii. So first I need to know how to convert the HEXA code in EXTENDED ASCII (because maj on letter A (not a )).(extended ascii is 8-bit ASCII characters) If I try to send fprintf(s,'¡') or fprintf(s,'%s','¡') nothing happend. (BTW '¡' is for A1 from hexa to extended ascii) If you have an idea.. Best regards stan

[Stan sdsd]

I have used char(sscanf('A1','%2X').') it seems to work, but now I need to send that ascii code... How ? Need help pleas

[Stan sdsd]

Okay, sending A1 or A2 or C1 is easy, but the A3+4octet, to set the speed I cannot understand, because with my code, I cannot transform A30200 into ascii, nor A3+0200.... I don't know what to do now

[Cedric]

What happens if you execute for example:

 fprintf(s, '%s', 'A0') ;
 fprintf(s, '%s', 'A40500') ;
 pause(2) ;
 fprintf(s, '%s', 'A40000') ;
 pause(2) ;
 fprintf(s, '%s', 'A4-0250') ;
 pause(4) ;
 fprintf(s, '%s', 'AA') ;

[Jan]

I suggest to post a copy of the descritpion in the documentation. Perhaps you misunderstand a detail and following your explanations will reproduce this misunderstanding instead of comming to a revelation.

My suggestion: fwrite(s, sscanf('A30020', '%2x'), 'uint8') interprets every 2 characters as HEX value and sends the corresponding value as byte to the interface. Perhaps you need '%.2x' (I cannot run Matlab currently). Is this successful?

[Stan sdsd]

You have the documentation in the web adress given in my first post (pdfcast). I have read it a thousand time. But yesterday I have learn somenthing HUGE : People how write this protocole made a huge mistake : the code they give (A2 for instance), is in HEXA !!!! .... But need to be send in EXTENDED ASCII (8-Bits). So I have used this code to transform my actual order (A2 again), in ascii, and then send it to the motor. It works for some order, and for some it don't. Where I block, is when they say, to paramater the spped, you need to send in ascii code, this hex code : A3+4 octet. And apparently, 0020 is for 2 km/h, 0002 is for O.2 km/h. So I tried to convert A30020, to set the speed at 2 km/h, but the convertion doesn't work, I have a square, that apparently meaning, 0020 is OUT of my extended ascii table present in nativ in matlab. Here is the code for conversion from HEX to ASCII (orders list is in the pdf form the first post) char(sscanf(String,'%2X').') If you have an idea. Maybe I have to send first 'A3' and then "02O00" as bytes... do not know ! * Best regards * stanislas

[Jan]

@Stan: Is this the complete documentation? 1 page only and there is only a French version?!

I still got no answer to my question, if fwrite(s, sscanf('A30020', '%2x'), 'uint8') works.

[Stan sdsd]

So sorry, I tried it yesterday, with no succes. And no, just french documentation saddly (and as you can imagine, explanations in it are so BAD :( )

Answer 2

[the cyclist]

If you look at the documentation for the command fprintf()

>> doc fprintf

you should be able to find the complete description of what that format specification is. Have you looked at that already, and still feel you don't have a good description?

Depending on what MATLAB version you have, to may have to expand the "formatSpec" section of that doc file.

[Stan sdsd]

I Have see this source, but I don't understand, why does it work in my situation ? I mean, I want to send ascii, and I thought fprintf with %s was enough, but it has never work ! and today I try this, and it works for some of my order (like A2 etc...) That's my question : why is it working for sending my ascii order. Anyway, thank you for your answer, I will go check the formatspec. My matlab version is the 7.8.0 R2009a Best regard "the cyclist"