The Control System Toolbox supports the use of both continuous-time and discrete-time models.
The syntax for the creation of a discrete-time model is similar to that for a continuous-time model, except that you must also provide a sampling time.
Sample Time = 0.1 sec
You can specify a discrete-time transfer function model by providing a sample time argument to the TF command:
num = [ 1 -1 ];
den = [ 1 -1.85 0.9 ];
H = tf(num,den,0.1); % Ts = 0.1 sec
You can also specify this model as a rational expression of z:
z = tf('z',0.1); % Ts = 0.1 sec H = (z - 1) / (z^2 - 1.85*z + 0.9);