CCS/TMS320F28069: Error occurred while executing External Mode MEX-file 'ext_comm':

Tool/software: Code Composer Studio

Hi all,

I am working on external mode interface of  matlab simulink with c2000 piccolo micro controller(TMS320F28377S LAUNCHPAD)

I COULD NOT SEE the signal properly in TIME SCOPE in simulink environment.

matlab version 2017b and ccsv6.

and i gave a SQUARE WAVE to the ADC  from the function generator with a frequency of 10 kHz.

Here, I am supposed to get a square  but not getting it in the scope.

But , When I give a sine wave to DAC ,I could see it nicely in the oscilloscope and again if i give this back to the ADC then the same TIME SCOPE has shown a good sine wave.I don't know what is the problem here.Please help me how to replicate the external signal in the TIME SCOPE when i connect the external signal to the ADC. 

Here I have attached the screenshots of the system parameters and  the improper square wave seen in the TIME SCOPE.