My understanding of your question is that you want to have a variable which change with every time step.So do that you do not a Data Store Memory Block , what you can do is provide a Input array of Pulse along with the time in your simulink model.
Ex : your time steps is 0.1 so , our time array will be
similarly let's assume our pulse be random(for example , we can any have values ):
Now to connect these inputs to simulink , go to Modelling->Model settings->Data Import/Export.
You would se ethis expression [t u], here t stands for our time array and replace u with pulse and apply the settings .
Now use the Input port block in simulink and connect this to your Function block.