Why Does a CompactLogix 5380 MSG to MicroLogix 1100 Fail?

A CompactLogix 5380 in dual-IP mode does not use CIP port 2. Its Ethernet ports are CIP ports 3 and 4, so a MicroLogix 1100 reached through port A2 needs the path 4, 192.168.3.40 with nothing after the IP address. The command must be SLC Typed Read, not CIP Data Table Read. If the MSG still errors once path and command are right, delete it and build a new one. An MSG edited repeatedly online can carry corrupted configuration.

The case below uses a 5069-L310ER on firmware 36.011. Port A2 is at 192.168.1.250 with gateway 192.168.1.1, and A1 is unaddressed and unused. The MicroLogix 1100 (Bulletin 1763, Series A) is at 192.168.3.40 with gateway 192.168.3.1, at a different facility reached across an ISP link. The MSG reads N20:0. The same method applies to a MicroLogix 1400.

Read the Error Before You Touch the Path

Start here. Each failed attempt tells you which layer rejected the request. Record .ERR and .EXERR from the MSG control tag before you change anything.

Path / command tried	Symptom	Actual cause
2, 192.168.3.40	Communication error	Port 2 is the single-IP port number. It does not exist as an egress port in dual-IP mode.
1, 1, 2, 192.168.3.40	Path rewrites itself to Analog_Input, 2, 192.168.3.40; parameter or communication error	Port 1 is the local backplane and slot 1 is an I/O module. Studio 5000 swaps in that module's name. You are routing into an analog card.
0, 1, 2, 192.168.3.40	Error in module configuration	Port 0 is not a valid egress port for this route.
4, 192.168.3.40 (existing MSG)	Extended error 315, Invalid segment type	Bad tag or data table syntax: a CIP tag command aimed at an SLC-style address, or a corrupted MSG configuration.
4, 192.168.3.40, 1, 0 with SLC Typed Read	Error 16#0013, Configuration Data size too short	An extra backplane/slot hop after the IP. The MicroLogix has no chassis to route into.
4, 192.168.3.40, 1, 0 with CIP Data Table Read	Class or instance not supported	Wrong command type plus the extra hop.
4, 192.168.3.40 with a new SLC Typed Read MSG	Data flows	Correct port, correct command, clean instruction.

How to read that table:

• Communication errors point at the path or the network.
• Segment, class and instance errors mean the packet arrived and the target rejected its contents.
• Once you see 16#0013 or "class or instance not supported", the IP route works. Stop debugging the network.

Understand Why Port 2 Fails on a Dual-IP 5380

A MSG path is a list of CIP port/address pairs, read left to right from the originating controller:

• Single-IP mode (linear/DLR): the embedded ports share one IP address and act as CIP port 2, like every earlier ControlLogix Ethernet interface.
• Dual-IP mode: each physical port gets its own IP address and its own CIP port number, 3 and 4. A1 maps to 3 and A2 to 4.
• Port 1 is always the controller backplane. 1, x means "go to slot x of my own rack."

A path is only valid relative to the controller that sends it. 1, 1, 2, 192.168.3.40 worked from another PLC on the 192.168.3 subnet because that chassis had an Ethernet interface in the slot the path named. Pasted into the 5380, the same hops point at a local analog input module. That is not a MicroLogix problem. Rebuild every path from the sending controller's own topology.

The target end of the path matters too. A MicroLogix 1100 is a standalone Ethernet node with no backplane behind it. The path ends at its IP address. Appending 1, 0 asks the MicroLogix to forward into a slot it does not have. It rejects the request with 16#0013 or a class/instance error, depending on the command.

Match the MSG Command to the MicroLogix Data Table

Get the command family right before you worry about data types:

• CIP Data Table Read/Write are CIP tag commands. They read and write native Logix tags by symbolic name. A MicroLogix has no symbolic tag table, so the request fails. Extended error 315 Invalid segment type is the usual result.
• SLC Typed Read / SLC Typed Write address PCCC-style data files (N20:0, F8:0, B3:0). Use these for MicroLogix 1100 and 1400 targets.

Configure the destination to match the source file:

• N files are 16-bit integers. Use an INT or INT[] destination. DINT and REAL destinations add a type mismatch on top of every other variable.
• Set Number of Elements to 1 for a single word. Size it to the array length for block reads, and stay within the file length set in the MicroLogix project.
• Confirm that file N20 exists in the MicroLogix program and contains at least the element you request.

Prove the Routed Path, Not Just the Ping

These two facilities are on different subnets, joined across an ISP. The controller sends through its own gateway 192.168.1.1. That router must route to 192.168.3.0 and pass TCP 44818. The MicroLogix gateway 192.168.3.1 must also route replies back to 192.168.1.0.

These checks waste your time:

• FactoryTalk Linx browse: the browser finds devices with a broadcast List Identity request, and replies come back over ordinary TCP. A device can appear in RSWho yet stay unreachable to messaging or HMI traffic on a different logical subnet without a proper router.
• ICMP ping: a ping proves Layer 3 reachability only. Firewalls and VPN policies often pass ICMP and block TCP 44818, or the reverse.

Use these instead. Plug a laptop into the controller's subnet with an IP address and gateway on 192.168.1.x, then run in PowerShell:

tnc 192.168.3.40 -p 44818
tnc -traceroute 192.168.3.40

• TcpTestSucceeded : True means the EtherNet/IP port on the MicroLogix answers across the routed path.
• The traceroute shows each router hop. A stall at the first hop points at the local gateway. A stall past the ISP edge points at the tunnel or firewall.
• If the link uses NAT, the MSG must target the translated address the controller sees, not the MicroLogix's local address.

Rebuild the MSG Instruction

Do not keep editing the MSG that has already failed several ways. After you have changed configuration repeatedly online, a new instruction is faster than hunting for residue.

1. Confirm the port mode in the controller properties. If dual-IP is active and only A2 is addressed, the path starts with 4. If you switch to single-IP (linear/DLR), the path starts with 2.
2. Delete the old MSG instruction and its MESSAGE control tag. Do not copy and paste them. A copy carries the old configuration with it.
3. Create a new MESSAGE tag and a new MSG instruction.
4. Configuration tab: Message Type SLC Typed Read. Source Element N20:0. Number of Elements 1. Destination Element an INT tag.
5. Communication tab: type the path 4, 192.168.3.40 by hand. Nothing goes after the IP address.
6. Make the edit offline and download it if your process allows. If you must edit online, finalize once instead of iterating on the live instruction.
7. Trigger the MSG from logic that waits for .DN or .ER before retriggering, for example a timer gated by the MSG status bits. Do not fire it every scan.

Verify the Read End to End

1. Watch the control tag. .EN goes true on trigger, then .DN sets with no .ER. .ERR and .EXERR stay at zero.
2. Go online to the MicroLogix with RSLogix 500 and read N20:0. The CompactLogix destination INT must show the same value.
3. Change N20:0 on the MicroLogix side. Confirm the destination follows within one MSG cycle. This proves live data, not a stale value left from an earlier attempt.
4. Let the MSG run for a period and monitor the .ER count. Intermittent errors across an ISP link point at the WAN, not the instruction.
5. Before you add SLC Typed Write messages, repeat the check in the other direction. Confirm that writes land in the intended file and that the MicroLogix logic does not overwrite them.

Avoid the Recurring Traps

• Borrowed paths: a path that works from another controller, or from RSLinx on a laptop, encodes that device's ports. Rebuild it from the sending controller outward.
• Auto-rewritten paths: if Studio 5000 replaces a port/slot pair with a module name, you have routed into your own I/O rack. Treat the rename as a fault flag.
• Port renumbering after a mode change: switching between dual-IP and single-IP changes the valid first hop from 3/4 to 2. Every MSG path needs updating after the change.
• Trailing backplane hops: 1, 0 belongs on paths into a ControlLogix chassis. It never belongs after a MicroLogix IP address.
• Wrong command family: CIP Data Table commands are for Logix-to-Logix tag messaging only.
• Corrupted MSG configuration: this is uncommon, but it happens after many online edits. If the path and command are provably correct and the error persists, replace the instruction before you blame the network.
• Messaging disabled on the target: verify on the MicroLogix channel configuration that messaging is enabled. In this case it had already been confirmed, so it was not the cause.

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