MSG Instructions, MicroLogix 1100 to CompactLogix 1769-L32E

Hello All,
I have a total of (8) prox switches that I am monitoring (1 for each machine) with a single MicroLogix 1100 controller.
I have (8) CompactLogix 1769-L32E all with different IP Addresses. Each CompactLogix needs to receive (1) of the (8) prox inputs from the MicroLogix 1100 and I would like to communicate via Ethernet using the MSG instruction. I have little experience with the MSG instruction and would appreciate any input or examples of how to do this. My guess is a MSG read from each CompactLogix and a MSG write from the MicroLogix 1100.

Not overly difficult however you are better off messaging from the CompactLogix rather than from the MicroLogix. Not that either one is difficult however if you message from the MicroLogix to the CompactLogix you have to setup a table in the CompactLogix to link the file types used by the MicroLogix to the tags used in the CompactLogix. When you go the other way you don’t have to setup any tables in either PLC. Here are a couple of manuals that should point you in the right direction.
http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm012_-en-p.pdf

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1763-rm001_-en-p.pdf

I second the motion of doing a READ from each CompactLogix instead of a WRITE from the 1100. I prefer to always do a READ whenever possible so you do not have "magically" changing data when you go online with the written to program.

Welcome to the Forum !

I agree that it is easier to write and edit and test MSG instructions in the CompactLogix than it is in the MicroLogix, if this were my system I would be doing the messaging in the MicroLogix.

First, doing the messaging in the MicroLogix allows for the most efficient transfer of data and for the shortest time between a proximity sensor data change and the arrival of that data in the CompactLogix.

It's most efficient because you don't have to perform the MSG repeatedly to get an update, but rather can trigger the MSG when the proximity switches change state.

That's also why the time delay can be as short as possible; in general, triggering based on and event is called "Change of State" or "Event Driven" messaging.

I would write more than one word from the MicroLogix to the CompactLogix, and make the first Word a rolling watchdog value. The CompactLogix will be able to monitor the changes in that watchdog value to know that the MicroLogix has stopped transmitting.

That, too, could be faster and more efficient because watchdogs are (generally) fast and network timeouts are (generally) slow.

Another note; the MicroLogix 1100 supports 32 total TCP connections; 16 incoming, and 16 outgoing.

In the system that the OP has described, the MicroLogix would probably be doing just the 8 outgoing connections, so it has plenty of capacity. An RSLinx session would be common to an RSLogix 500/RSLinx instance, so that's just one incoming connection.

But don't plan on making this MicroLogix into the communications hub of the control system and adding a couple dozen more controllers to its workload.

And another thing; I noticed the OP mentioned "a Write in one controller and a Read in another". The ordinary MSG instruction doesn't work that way; the controller that's receiving the command does not have to be configured with any ladder logic instructions.

If the CompactLogix is the receiver of the MSG from a PLC-5, SLC-500, or MicroLogix, it does need to have its "PLC/SLC Data Table Mapping" feature configured. See the Help file in RSLogix 5000, or do a Forum search for detailed explanations of how that works.