simatic s300 ladder strange.

When exploring  existing  working  PLC  program    i   found  rung  (on  pix).

PLC  cpu   is  writing  to  input   bits  .

Input  bits  used  by  this  rung  are  not  mapped  to   any  inputs  hardware.

Please   explain   what is  being  done  here.

ziggypi

When exploring  existing  working  PLC  program    i   found  rung  (on  pix).

PLC  cpu   is  writing  to  input   bits  .

Input  bits  used  by  this  rung  are  not  mapped  to   any  inputs  hardware.

Please   explain   what is  being  done  here.

Not every piece of one man's creation
can be understood and explained
by another who did not know him.

You are making this guessing game extremely difficult. An important piece of the puzzle would (for example) be to know if those bits are used anywhere else. It may even be part of a bigger BYTE / WORD / DWORD that are read / written to.

Those bits have "coil" in its name which feels more natural as outputs. Yet it is inputs which are written to. These are placeholders. Now comes the question if it is of pieces of undeveloped code or pieces of communication words.

Hello.

What you shared does not add to the insight.

I theorize that those inputs are reserved for another function that is not available in the system you have. I would even think that there are more inputs/outputs/memory that is used in this way that has no actual connection with the outside world.

There are some truly mad-scientist-genius things that you can do with the S7-300 / S7-400 PLC to hide some functionality. That kind of thing can only be identified by people who knows what they are looking for and has unrestricted access to the program and hardware.

If you monitor those inputs and those change at times.. then you can worry. Else see those as reserved bits and move on.

Regards.