Communication Help Requested

I was wondering, i have been watching several threads regarding places where they have more than one brand and/or type of PLC running and they wish to gather data from all the different PLC's. While my question is somewhat similar in nature it also contains differences.

2 different PLC units. Unit 1 is a Horner NX 221. Unit 2 is a Mitsubishi Q series PLC.

What I want to accomplish is to get the two of these units to talk back and forth and share certain aspects of data. Some of the data will be nothing more than Boolean Bits, other will be Double Ints. I also want it to be somewhat robust and almost bullet proof. One of the key things that would be great to have is that since the PLC units will be in close proximity to one another whatever creates the link between the two should also be there. This way even if the Network of server goes south the two plc's will be able to maintain communication and connection.

So with that being said I was wondering what all ideas other people have come up with to solve such a dilema?

Thanks and have a great day.

Use a small HMI panel that can talk to both PLCs and have it read from one and write to the other. You don't necessarily have to display any screens on the HMI, but it might be nice to display an error message when it is not communicating with one or both PLCs.

If digital I/O is available and a network is not feasible or economical, bit-banging the data is a crude but workable method. Essentially one would build a ladder version of a parallel interface. Not pretty but it would get the job done.

I've seen it done (I didn't do it) and multiple bytes were moved one byte at a time. The receiving device constructed the bytes together as needed.