How to merge two characters into one in Matlab Simulink

Hello,

I am new and i am struggling with merging two inputs into one after some conversion process. It was easy at normal matlab .m file execution, while i am struggling with the Simulink as it doesn't take "num2str" command and giving error. Can anyone guide me how to merge two values. I will share the .m file code with you guys just for reference.

R(i,1:68)=read(device_T,68,"uint8");
Time(i,1)=(i*delay);
%RC_ROLL
RC_ROLL_LSB= dec2hex(R(i,26)); %26 25
RC_ROLL_MSB= dec2hex(R(i,25));
RC_ROLL_Comb= strcat(num2str(RC_ROLL_LSB),num2str(RC_ROLL_MSB));
RC_ROLL(i,1)=hex2dec(RC_ROLL_Comb);

this read the serial and save require data accordinly to it for later use and graph plotting. This is the simulink function code:

function RC_ROLL  = fcn(R)
%RC_ROLL
RC_ROLL_LSB= R(26); %26 25
RC_ROLL_MSB= R(25);
RC_ROLL_Comb= strcat(num2str(RC_ROLL_LSB),num2str(RC_ROLL_MSB));
RC_ROLL=hex2dec(RC_ROLL_Comb);

and this is the model picture:

and this is the error:

num2str is supported only for constant inputs. Consider using sprintf instead. Function 'MATLAB Function' (#30.104.124), line 5, column 22: "num2str(RC_ROLL_LSB)" Launch diagnostic report.

Component:MATLAB Function | Category:Coder error

Undefined function or variable 'RC_ROLL_Comb'. The first assignment to a local variable determines its class. Function 'MATLAB Function' (#30.164.176), line 6, column 17: "RC_ROLL_Comb" Launch diagnostic report.

Component:MATLAB Function | Category:Coder error

Errors occurred during parsing of MATLAB function 'Modelll/MATLAB Function'

Component:MATLAB Function | Category:Coder error

Simulink cannot determine sizes and/or types of the outputs for block 'Modelll/MATLAB Function' due to errors in the block body, or limitations of the underlying analysis. The errors might be inaccurate. Fix the indicated errors, or explicitly specify sizes and/or types for all block outputs.

Thank you in advance.

Answer 1

[dpb]

function RC_ROLL  = fcn(R)
  RC_ROLL=double(256*uint16(R(26))+uint16(R(25)));
end

Of course, that's what your m-file version should do, also...there's no need for the overhead to turn back into string and then reconvert to numeric so that Simulink doesn't allow num2str() is no issue.

Of course, as the hint in the error message says, you can do the same thing as num2str() with sprintf(), just have to use a specific format string instead of letting it default -- but here there's no need for either.

[Walter Roberson]

It looks like the input is the result of a binary read in uint8 mode, so you might need

function RC_ROLL  = fcn(R)
  RC_ROLL = 256*uint16(R(26)) + uint16(R(25));
end

[dpb]

Yeah, you're correct Walter, forgot about that while fixing up original...the unit8 will saturate.

Made change/fixup in Answer...that would return a uint16() result; the original using hex2dec() would return a double so probably should cast there, too.

I'm not sure if Simulink would transparently handle that or not, never had access to it...

[Muhammad Amir Khan]

Thank you so much for your input and quick response, really appreciated. Yes it solved the issue.