How to do STFT and plot the spectograms without using functions?

[sdk324]

Hi i am not very familiar with Matlab.
I have to do a small project wherein we have to do the STFT and plot the spectrograms.

But we are not allowed to use the specgram function of matlab directly.

Can somebody help us and let us know how we can do the same without using function.

Thanks.

 

[yella]

I have seen many links but no one is that clear about use of spectrograms in STFT using linear chrip signal..I tried it out in simulink am getting error