Solving system of ODEs and signal generator function in Simulink

I have a simulink model with a system of four coupled ODEs (represented using four simulink function blocks) and a signal generator (sine wave) block. The signal generator serves as the input to the system. Now I am confused how can I denote this signal generator function in other differential equation functions. Is it the same u(1), u(2) ..? And, how can I input it to other function block of ODEs. Since signal generator is not an algebraic equation, I cannot consider it as a differential algebraic equation.