One of the questions in our final exam will be "Explain the need of A/D and D/A converters in digital controllers".
I could not find the reason anywhere why the Plant part of a block diagram requires a continuous signal. Isn't it supposed to receive a digital signal and output a digital signal? What inside process needs an analogue signal and why? This lack of understanding is probably because I do not understand what Plant is for at all.
I also do not understand why A/D converter is not immediately after the Plant block, but only when it returns back to the start of the block diagram. Isn't a digital controller supposed to output a discrete signal?
Here is a general block diagram of a digital control system :