Assembly program to stop stopwatch counter if a key is pressed and show the stopwatch count

Assembly program to stop stopwatch counter if a key is pressed and show
the stopwatch count

I am trying to design a stopwatch program on assembly using M/Tasm syntax
as my own personal project that first displays the system time and prints
it and then later on act as a stopwatch. If the user presses 's' at
runtime, the program will show the hh:mm:ss passed since the stopwatch was
started and then display the result. I have successfully designed the code
to get system time, display it, and execute a proper stopwatch. Problem is
I can't manage to stop my stopwatch at runtime and then display the time
passed in hh:mm:ss. Anyone with any ideas? I can't paste my code here on
SO or else my code will be used by others, It is a long code, Please
understand, that I have my reasons for this :).
Thank You.. just asking for ideas, not the code :)