Resolving CJ1M Ethernet Connection Failure in CX-Programmer v8

Problem Overview

When commissioning a CJ-series modular PLC (typically a CJ1M with a CJ1W-ETN21 Ethernet unit, or a CP1L series with -ETN suffix) using CX-Programmer v8.x, technicians frequently encounter a state where:

• The host PC can ping the PLC IP address successfully (e.g., ping 192.168.250.4 returns replies within 1 ms).
• CX-Programmer returns "Conexión fallida" (Connection Failed) when invoking Online Node → EtherNet/IP with only the destination IP.
• The PLC's RD (Receive Data) and SD (Send Data) LEDs blink synchronously at roughly 1 Hz, but the session never completes.
• The fault repeats whether the PLC is connected directly through a crossover cable or through a switch with straight-through cabling.

These symptoms indicate a FINS routing or project-mapping problem, not a layer-1/link fault. Reachability at the IP layer is intact, but the application-layer handshake (FINS/TCP or EtherNet/IP) never negotiates because CX-Programmer cannot resolve a valid FINS source/destination pair on the host PC.

Affected Hardware, Firmware, and Software

Root Cause Analysis

CX-Programmer's Online Node connect path uses a flat, host-only FINS routing table stored in the Windows registry under:

If the host routing table lacks the destination IP / FINS node pair, Online Node → EtherNet/IP fails even when L3 connectivity exists. "Online Node" is meant for transient ad-hoc connections where routing has been pre-populated, typically by CX-Integrator or a previous successful CX-Programmer project.

For a stable project-target configuration, CX-Programmer expects the user to declare the network inside the project:

1. Create (or open) a project whose Device Type matches the CPU faceplate.
2. Open Change PLC, confirm CPU type, then open Settings → Network.
3. Select Network Type = Ethernet (not "None" or "Toolbus").
4. Under Ethernet, open Controller, then enter IP Address = 192.168.250.4.

When the user invokes Online Node → EtherNet/IP directly without a project, CX-Programmer sends a FINS/TCP frame to UDP/TCP port 9600. The PLC's ETN unit sees a FINS node it does not recognize (because the PC's routing table points nowhere) and rejects the session. The RD/SD LEDs blink because ARP/ICMP traffic is fine but every FINS frame increments a FINS node error counter on the unit; the blinking reflects the rejected-but-not-dropped frame stream.

Prerequisites

Step-by-Step Resolution

5.1 Create or repair the project

1. Launch CX-Programmer.
2. Select File → New. Name the project (e.g., CJ1M_EthOnline.proj).
3. From Device Type, select CJ1M (or CP1L/CS1G/CS1H matching the faceplate).
4. From CPU Type, choose the matching CPU (in the original field report, the model selected after the fact was CPU13).
5. Click Settings; confirm the Network tab shows Network Type = Ethernet before saving.

5.2 Configure the network type inside the project

The fix that ultimately worked in the field was to declare the network inside the project, not at "Online Node":

1. Right-click the project icon in the project workspace.
2. Select Change PLC. This reopens the same wizard used at project creation.
3. Confirm Device Type = CJ1M.
4. Confirm CPU Type = the model selected in 5.1 (e.g., CPU13 for CJ1M-CPU13).
5. Open Settings and select the Network tab.
6. Change Network Type from its default (often None on a fresh project or Toolbus if migrated) to Ethernet.
7. Under Ethernet settings, click Controller → set IP Address = 192.168.250.4.
8. Set Source IP explicitly to the host NIC if the PC has more than one IPv4 active (e.g., 192.168.250.2).
9. Click Apply, then OK; save the project when prompted.

5.3 Verify project side before testing

1. Switch CX-Programmer to Online mode (toolbar button or Ctrl+W).
2. Watch the status bar — it should progress from Connecting to Connected to CJ1M CPU13 on Ethernet.
3. If the dialogue still fails, open PLC → Communications and verify that Network Type: Ethernet (FINS/TCP) is selected (CX-Programmer v9.x and later offer an explicit FINS/TCP option; v8.21 defaults to FINS/UDP).

5.4 Switch back to Online Node if you still need ad-hoc

After the project-driven connection succeeds, CX-Integrator's network browse populates a routing entry, and from this point Online Node → EtherNet/IP also succeeds because the host routing table is now set.

Verification

After applying the project-level network fix, run a sequence of checks:

1. Click Connect Online. The status bar should show Connecting to CJ1M CPU13 on Ethernet... → Connected.
2. Select PLC → Transfer → To PLC. Browse sections (PC, PLC, Comments, Program) should populate with the destination CPU.
3. Open PLC Information (Ctrl+Shift+I) and confirm CPU model, CPU unit version, and the ETN-unit's firmware (the firmware character string is shown on the right pane of the CX-Programmer status window).
4. Switch the PLC to Monitor mode (PLC → Mode → Monitor) and confirm the lower-right pane shows "Monitor Mode".
5. Toggle a single output on/off from the project and confirm the physical LED on the output module follows.

If the LEDs blink synchronously again, return to Change PLC → Network and re-verify both IP Address (PLC target) and Source IP (host NIC).

Rotary Switch and IP Configuration Reference

For ETN21 firmware versions V2.0 and newer, FINS/TCP and UDP/TCP port numbers are configurable; the default is 9600. CIP/TCP listens on 44818 and CIP I/O discovery on 2222.

Network Type Differences in CX-Programmer

The user's remedy worked because the project-defined connection path populated the routing table implicitly, so CX-Programmer no longer depended on the empty Online Node entry.

LED Diagnostic Indicators

If RD and SD blink in tandem at approximately 1 Hz while CX-Programmer is connected but never settle into a steady RD-only pattern, treat the symptom as a routing or FINS node mismatch. Run CX-Integrator → Network → Connect to Network → Ethernet → Resolve Network and confirm the discovered device shows the same IP and firmware version as the physical unit.

Routing Tables, FINS Ports, and CX-Integrator

CX-Integrator is the dedicated tool for FINS routing across multiple subnets. On a single-segment Ethernet network it still matters, because it can:

1. Discover all FINS nodes reachable via UDP 9600 broadcast.
2. Edit the host routing table so CX-Programmer and any OPC server can talk FINS reliably.
3. Bind the destination FINS node (1–254) used by Online Node.

To verify routing after the project fix:

1. Open CX-Integrator and select Network → Connect; choose Ethernet.
2. The right pane should list 192.168.250.4 and the corresponding CPU type (CJ1M, CP1L-M, CS1G, etc.) within a few seconds.
3. Right-click the discovered PLC and select Set as Destination Network; assign a local network number (0–127) and a PLC node matching the CPU faceplate rotary (e.g., 4).
4. Save the routing table. CX-Integrator writes to HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\OMRON\CX-Server\FINS\RoutingTable.
5. From this point, Online Node succeeds because the routing entry exists; subsequent CX-Programmer projects can also rely on the same table.

Multinetwork engineering: when the PLC and PC are on different subnets (e.g., PC at 192.168.250.0/24 and PLC behind an Ethernet/IP router at 192.168.251.0/24), CX-Integrator's Routing Table Editor must include the intermediate router as a "gateway" entry. Without this, FINS frames are dropped at the first hop even when ICMP succeeds.

Common Pitfalls and Edge Cases

Safety and Network Hygiene

• Place CJ1M and ETN21 on a control LAN or VLAN isolated from corporate traffic; many PLCs have no built-in authentication on FINS/UDP 9600 and will respond to anyone on the segment.
• Disable the ETN21's web server in production unless actively used.
• Document the static IP, FINS node, and routing table in the project's README.txt; the rotary-switch node is often the only thing rescue crews need during an outage.
• Verify PLC programs against Omron's documented limits before download; 16K-step variants (CJ1M-CPU13 / CPU23) have I/O table sizes that older project files can exceed.