[ First "C" not C++ 8052 also available in Pascal,Forth and BASIC.
Since the AT89C52 does not have an A/D or D/A these would have to be added. OR are your inputs / Outputs 0 and 5 Volts? That would be simpler. Does the hardware exist? Is this a school project? What is the budget?
If you post more details,you will get more feed back. ]

Ok. C then < *(we thought it might turbo c++ which shows you why we nee help).
The inputs should be from sensors which will be a voltage. There shouldn't be spikes but it wouldn't hurt to buffer it perhaps with AND gates? (we don't know these things that you guys do so we are thinking out loud in a way). We would think that since sensors are providing the input that the input voltage would be fairly steady and gradually change over time. So yes a a/d and d/a might be needed in on front and back to achieve the output of 0 or 5 volts output.
No hardware as yet (or what are you asking?). Not a school project but a personal project. Budget is slim which is why we are asking for help.
j.