The MSG instruction in the ControlLogix is very powerful, but can be intimidating the first time you use it, especially the "Path" entry.
First, be sure that RSLinx can "see" the remote 1756-ENET module on the VPN-connected TCP/IP network and can browse down to the PLC-5 controllers on the remote DH+; you won't be able to get a MSG instruction to work if RSLinx won't work from the same Ethernet network as your originating controller.
Next, be sure that the PLC-5 controllers on the DH+ all have the same "Link ID" setting on their DH+ ports. Because it's not used in local DH+ messaging, the majority of DH+ users ignore this setting and leave it at it's default value of 2.
RSLinx can browse without it, but a MSG instruction and 1756-DHRIO configuration need that value. Configure the Channel A or B that is connected to the DH+ on your 1756-DHRIO (right-click in RSWho and go to Module Configuration) that is connected to the DH+ to be the same "Link ID" as the PLC-5's on that network.
Now, we can take on the MSG instruction and it's Path entry in the ControlLogix CPU. The Message Type for my example will be a PLC-5 Typed Read.
The Path instruction for a DH+ Message needs to guide the MSG across backplanes, through modules, across networks, and right up to the 1756-DHRIO in the remote Logix chassis. The Channel, Link, and Remote Node entries take the message from there.
For example, our theoretical message has to go through the following steps:
1. From the Logix CPU to the backplane.
2. From the backplane to a 1756-ENET module in Slot 5.
3. From the 1756-ENET Module on to an EtherNet/IP network.
4. From the EtherNet/IP network to a remote IP address (192.168.1.102) for another 1756-ENET.
5. From the 1756-ENET to the backplane.
6. From the backplane to a 1756-DHRIO in Slot 3.
7. From the 1756-DHRIO to the Channel A DH+ netowrk
8. From DH+ to the PLC-5/20 at node 14.
I know the following Path Entry codes from reading the RSLogix 5000 help file: "1" is the hop to the backplane, and "2" is the front port of any single-port network card. Slot numbers are slot numbers, and addresses are addresses.
In a theoretical system described above, the Path would be:
"1, 5, 2, 192.168.1.102, 1, 3"
The DH+ message additional info from the MSG configuration screen takes the message the rest of the way:
Channel A, Link 2, Node 14.
If you post some of the actual configuration of your system and the entries you've made in the MSG instruction, I'd be happy to review them.
