TCP/IP Ethernet communication on PLC

Question

I try to connect an Omron PLC (CP1L) to a PC through an Ethernet Option Board. I have setup connection correctly and is able to connect to the PLC to configure its IP and various settings.

Then I have problem getting the ladder program to run correctly.

Documentation indicates address A202.00 will turn on when communication is enabled, but when I simulate the ladder program, the address A202.00 always turn ON. Even when I disconnect the Ethernet cable, the address remain turn ON. I do not understand why the address remain turned on even there is not ethernet cable connecting the PLC and the PC.

Simulated ladder program indicates A202.00 always turn ON:

Answer 1

If you have the physical PLC then why are you running in simulation? If you want to debug the real system just plug into it with a USB cable and use "PLC -> Work Online...". I don't think networking simulates exactly right since the simulator itself uses simulated networking to work. In any case, if you are running in simulation then the state of the real ethernet port on the real PLC will have absolutely no impact on the simulation. It doesn't care that you even have a real PLC at all.

In any case A202.00 is just a "Port not busy" flag. You use it to guard rungs against trying to read/write from the same port at the same time or to trying to perform multiple simultaneous reads or writes. A202.00 is ON so long as the com port is not busy. If it is reading or writing then the A202.00 will go OFF for the duration of the read or write, preventing other communication rungs guarded with it from executing, and then returns to the ON state.