S-function builder variable output

Hello, I am making a project of induction motor control system, using s-function builder. I have a C code implemented in s-function builder but i have a problem with output. This code specifies that variables of the motor should change each simulation step time. In the output I only gets constant values and a straight line in the Scope... According to MATLAB documentation the mdlOutput is invoked at each simulation time step but it seems like it compute one time. Is it possible to make s-function builder which returns output computed at each simulation step time? Im trying to do it on a simple example like incrementing a variable and pass it to the output but im struggling with it... Have I need to use input, or discrete states? My professor said that it can be made without depending the input from output... Thanks for your answers!