Linking registers between two PLCs

I have two screens that run on ladder logic.

Each has the ability to start a process (We'll just call it ProcessA) and stop it as well with a push button.

However, both screens need to be aware of the state of the Process state (either running or not running).

The two screens communicate over ethernet global data (EGD) which is just a fancy way that says they each have registers they send to one another and receive from one another

I don't think they can send and receive the same register.

Therefore, I am wondering if anyone knows a way to link the two button states between the screens. I tried this but it doesn't work:

/* Remote Screen */

  Local_Selected        Remote_Selected

----(P)-------------------(S)-------



  Local_Selected        Remote_Selected

----(N)-------------------(R)-------



/* Local Screen */

  Remote_Selected       Local_Selected

----(P)-------------------(S)-------



  Remote_Selected       Local_Selected

----(N)-------------------(R)-------

My thought being that if the Remote screen saw the local screen's register go positive, it should set its own. Likewise, it should reset its own bit if it sees the bit drop to zero. (and vice versa)

However, it doesn't work.

What brand/model PLCs and HMIs are these?

Horner Nx251.

It's sorta PLC + HMI in one, depending on what I/O cards you have installed. However, the logic should probably be hardware independent.

So your problem isn't getting each to communicate to the other to properly pass the data, it's just to get the logic behind saying whether one is on or not?

Yep. Since both screens allow the user to turn the process on, I need to make sure the registers their UI elements reference are on the same page.

Wouldn't want the user to turn on the process at the back of the machine, and it say the process was off on the front.

Why don't you link them directly with the existing built in C-Scan Network?

This is specifically designed to share common data between units at high speed with minimal programming issues.
Did a project some years ago linking 15 units together, very reliable, very fast and easy to implement.

The two screens are pretty far apart (50-10ft. depending on machine) and that would probably require running a new set of wire + conduit down the machine. We are looking for a solution that allows us to update the functionality without additional material investment...