Discrete derivative Initial Condition

Hello everyone,

I am trying to convert a functional and reliable continuous model into discrete in order to develop a real time control for the actual prototype.

The main problem I am having at the moment is that the discrete derivative does not work as I expected. An initial condition is mandatory, then I have to get the initial condition from a signal and there is no option to input an external value into the block. I have tried to set a variable and read it in the initial condition without success.

In summary, how could I do a discrete integration setting the initial value equal to the input of the block?

Please help.