Step Transfer Function - give input, take output value

I would simulate and validate my pid microcontroller implementation in matlab.

I have some object described like eg.:

es = tf('s');

sys = 1 / (R1*C1*es + 1);

sysd = c2d(sys, Ts); % Ts=0.5

I would set initial value, put some input value, make something like a step, take output value and repeat everything in loop for calculating next input values.

How to do it? I tried edit lsim but there is no acutual source code.