How to implement pulse stimulus

Hi,

I hope some of you can help me with my problem in Matlab.

I am trying to reproduce results from a scientific paper, where they have been looking at different differential equations. I am using the ode23s solver without any problems. In the paper, they have used a parameter (xx) as stimulus. xx can be both a constant stimulus or pulse stimulus. I have no problem solving the differential equations system when xx is a constant stimulus. My question is how can I implement xx as a pulse stimulus? xx should have alternating concentrations of say 1 and 5, pulse duration of 50 s and period 150 s.

xx is part of an equation and the equation is part of one differential equation.

Thanks!