Some problems of Siemens S7-200 programming, please give me some advice!

The m storage area is 1. S7-200 has only 32 bytes from M0.0-M3 1.7, so it can be used at will without connection.

2. M of the module is connected to 0V, one end of the button or contact is connected to Ix.x, and the other end is connected to 24V.

3. Before triggering the reset instruction, it can be any bit, which can be the output of I, Q, M, T, V or other modules, such as comparison result, rising edge and falling edge.

4. If the program is simple, of course, it is not necessary, but it will be difficult for a slightly more complicated program not to use V storage area. After all, area M is too small, so it is not enough to need a little calculation.

5. Subroutines are unnecessary. When your program is too long to read in one place, or you have a function that needs to be reused, using subroutines can improve efficiency.