Butterworth filter code implementing Simulink block

Hello,

I'm working on fm demodulation. I managed to do this via Simulink but I would also like to do this with code. I'm at the moment when my modulation of FM in code and in Simulink is the same. For demodulation I use Butterworth filter and Continous Time VCO. Is there any code, which could implement the Butterworth filter for my signal, let it be y, with parameters same as in the Analog Design Filter Block? I tried butter() function but I get bad results