Simulink Arduino Analog Input frequency problem

Hi, i have a problem interfacing arduino with Simulink. I connect the Analog Input block to a scope block in my smiling model. The analog input is physically connected to a pulse generator with pulse period of 10ms. In my simulink model i set the Analog Input frequency to 1ms. If i start an external simulation of 0.2 seconds the result on the scope is just some "HIGH" values point with a random distance one from the other. I have already set in the model configuration parameter the fixed step solver (ode3) with a fundamental sample time of 1ms. How can i have a decent result? Thank you