The landlord listens to me, don't listen to their nonsense. I basically get full marks in PLC and fail in C language and single chip microcomputer, so C language has nothing to do with single chip microcomputer and PLC. Before learning PLC, you should learn some simple circuit knowledge, such as being able to understand normally open and normally closed circuits; Time relay, self-locking etc. This is the most basic, because these are also the basis of the ladder diagram of PLC, and then read your S7 book, starting with bit logic instructions and reading a few symbols, and then use these symbols to find problems. It is best to install STEP7 (programming software of Siemens S7) online at home, and then install PLCSIM (simulated field test software), and read more and practice more. If you can't find PLCSIM, leave your QQ and I can send it to you. Step seven, you'd better download it from the internet. Because it's too big to pass.

If there are still difficulties, I will be your first teacher.

To add a little more, if you go to work, you must not only understand the PLC program, but also use the software STEP7.