Two functions for same Arduino in Simulink

I have a Simulink diagram which contains 2 s-functions (or Matlab function) to control my Arduino. In first function i read serial port, in second one i write servo angle. So i have to define two different object for the same COM port and it gives error. My arduino has a code inside so i cannot use external mode or Arduino IO package.

I tried to make one decleration as global all around the diagram but it gives error because it is not one of the proper data types for data memory.

What should i do?