Troubleshooting NX1P2 EtherNet/IP HMI Timeout Errors

Troubleshooting NX1P2 EtherNet/IP HMI Timeout Errors

The Omron NX1P2 is a compact machine controller in the NJ/NX family that integrates sequence control, motion control, and EtherNet/IP communications into a single CPU unit. It is widely deployed where panel space is constrained but full Sysmac platform capability is required. A common field integration pairs the NX1P2 with one or more third-party HMIs (Wecon, Kinco, Weinview, Proface, Red Lion, Maple Systems) over EtherNet/IP explicit messaging, with the HMI as scanner polling PLC tag values. When that integration is left at default HMI polling parameters, intermittent "timeout" errors and full HMI lock-ups are observed even though the physical layer is healthy. This reference addresses the NX1P2 + 3rd party HMI timeout failure mode, explains why EDS file registration is not required, identifies the actual root causes (CIP connection budget exhaustion, polling rate overload, boot sequencing, switch behavior), and provides a verified resolution procedure.

Affected platforms: NX1P2-9B[][][], NX1P2-1040DT, NX1P2-1140DT, NX1P2-1240DT running Sysmac Studio projects that poll tags from any 3rd party EtherNet/IP HMI. Compatible controllers (NJ501, NJ301, NX102, NX502) follow the same diagnostic procedure but typically have larger CIP connection pools.

1. Failure Profile: NX1P2 + Wecon HMI Timeout Errors

The reported symptom signature is consistent across multiple field reports:

• Two Wecon HMIs (or comparable 3rd party panels) connected through an Omron W4S1-05D unmanaged 5-port Ethernet switch
• EtherNet/IP explicit messaging (HMI is the scanner; NX1P2 is the adapter)
• Intermittent "timeout" alarms displayed on either HMI
• Occasional full HMI lock-up requiring a manual power-cycle to restore communication
• Issue persists with only one HMI connected (rules out HMI-to-HMI contention)
• Sysmac Studio does not list the HMIs in the EtherNet/IP network view (expected when PLC is adapter)
• Sysmac event log may or may not show EtherNet/IP errors depending on the underlying cause

This pattern is the classic signature of CIP connection resource exhaustion combined with high-frequency explicit message polling. The NX1P2 has a finite CIP connection pool shared between every CIP client and server in the cell, and every active HMI poll consumes explicit message resources the CPU must service. When that budget is exceeded, the NX1P2 rejects new CIP connection requests with CIP error codes that the HMI driver surfaces as generic "timeout" messages, masking the underlying cause.

2. EtherNet/IP Connection Architecture on the NX1P2

The NX1P2 built-in EtherNet/IP port implements the Common Industrial Protocol (CIP) on top of TCP and UDP. Three CIP transport classes are relevant for HMI integration:

For HMI tag polling, the Wecon (and most 3rd party) panel driver typically opens Class 3 explicit messaging connections. Each connection remains open for the duration of the session; within each connection the HMI issues multiple read/write requests for individual tags or tag groups. The NX1P2 must dedicate CIP resources to each open Class 3 connection until the connection is explicitly closed (HMI logout) or times out from the CPU side.

The NX1P2's built-in EtherNet/IP port also supports UCMM (Unconnected Message Manager) for one-shot CIP messages; some HMI drivers fall back to UCMM when persistent connections fail. Both UCMM and Class 3 draw from the same CIP connection resource pool, so the budget is identical regardless of which transport the HMI uses.

The scanner / adapter distinction is critical when interpreting Omron documentation about EDS files:

• Scanner = the device that initiates CIP connections and I/O requests
• Adapter = the device that responds to the scanner

In a Wecon HMI polling an NX1P2, the HMI is the scanner and the NX1P2 is the adapter. The NX1P2 must be configured as a CIP adapter (server) on its built-in EtherNet/IP port, which is the default operating mode when no tag data links are configured in Sysmac Studio.

3. NX1P2 CIP Connection Budget and Resource Limits

Each NX1P2 CPU has a finite number of CIP connections supported by the built-in EtherNet/IP port. The exact value varies by part number and must be verified against the controller datasheet:

A single Wecon HMI typically opens between 4 and 12 explicit message connections depending on the configured screen count and tag group strategy. Some 3rd party HMI drivers open additional UCMM sessions during link-up attempts to discover available services before transitioning to Class 3. With two HMIs and a default Sysmac Studio connection pool, the CIP server connection count can saturate the available budget quickly, especially during repeated reconnects after a transient network glitch.

When the connection pool is exhausted, the NX1P2 begins rejecting new CIP connection requests. The rejection is communicated to the HMI using a CIP error status field inside the response packet, but most HMI drivers interpret any rejection as a generic "timeout" and retry, masking the true CIP error from the user. The NX1P2 itself may or may not log a corresponding event depending on firmware revision and Sysmac Studio event log settings.

4. Why EDS File Registration Does Not Apply

A recurring question in field deployments is whether EDS (Electronic Data Sheet) files for 3rd party HMIs must be imported into Sysmac Studio. The answer depends strictly on the role the NX1P2 plays in the CIP exchange:

In the Wecon HMI scenario, the NX1P2 is the adapter (server). The Wecon HMI is the scanner (client). Therefore no EDS registration is required in Sysmac Studio. The Wecon configuration software configures the connection entirely on its side, specifying the NX1P2's IP address, tag names, and polling rates. Sysmac Studio has no need to "see" the HMI as a device in its network view for the polling to work; the lack of visibility is correct behavior.

Similarly, the NX-EIC202 EtherNet/IP Coupler is exclusively a slice I/O adapter that allows NX-series slice I/O to sit on an EtherNet/IP network as an adapter device. It is not involved in HMI-to-PLC communication and is not a CIP scanner. Importing its EDS file does not change how the NX1P2 talks to an HMI, and adding the coupler to the topology provides no benefit for HMI integration.

5. Network Topology and Reference Architecture

6. HMI Polling Behavior and Tag Refresh Rate Analysis

Explicit message polling on EtherNet/IP follows a request/response pattern:

1. HMI opens a TCP connection to NX1P2 IP at port 44818
2. HMI sends a CIP Read request for one or more tags (single tag or symbol path)
3. NX1P2 services the request from its task scan queue
4. NX1P2 returns a CIP response containing the requested values
5. Connection remains open; subsequent polls reuse the same TCP socket

The interval between polls for a given tag is the tag's refresh rate, configured in the Wecon HMI software. Typical default values are 1000 ms (1 second). With N tags, this generates N explicit message requests per second per HMI, regardless of whether the tag value has changed.

Traffic calculation example:

The NX1P2's primary task scan time directly bounds the rate at which CIP explicit requests can be serviced. If the primary task scan period is 2 ms and each explicit message requires 0.3–0.5 ms of task time to service (read + response), then 4–6 CIP requests per task cycle is the theoretical ceiling before the scan begins to overrun. At 200 requests per second, that ceiling is reached within 5–6 task cycles — well within normal operation — but at 500–1000 requests per second the NX1P2 falls behind.

When the request rate exceeds what the NX1P2 can service within the HMI's expected response window, the HMI driver declares a timeout. The NX1P2 still processes the request, but the HMI has already moved on, and the next poll queues on top of the previous one, compounding the delay. Under sustained overload, the CIP connection pool is exhausted as requests back up and connections are not released in time.

Mitigations, in order of impact:

1. Increase the tag refresh interval in the Wecon software from 1 s to 2–5 s for non-critical tags
2. Group related tags into arrays or structures so a single CIP read retrieves multiple values
3. Reduce total tag count by moving screen-local values to the HMI's internal memory
4. Use symbolic CIP segments (CIP instance 0x6C) for variable-length tag reads rather than attribute reads (instance 0x0E) which return fixed-size attribute structures
5. Configure the Wecon driver to use UCMM for one-shot polls when the value is read rarely

7. Power-On Sequencing Between NX1P2 and 3rd Party HMIs

A frequently overlooked source of timeout errors is the relative boot time of the HMI versus the PLC. The NX1P2 boot sequence includes:

1. Power-on self-test (POST)
2. Hardware initialization (built-in I/O, EtherNet/IP controller, motion engine)
3. Loading of project from non-volatile memory
4. EtherNet/IP stack initialization and TCP socket binding
5. Mode change to RUN

This sequence takes 5–15 seconds from power-on depending on project size, the Sysmac Studio version used to compile the project, and whether the controller performs a full project verification on startup. The Wecon HMI typically completes its embedded OS boot and starts its CIP scanner within 2–5 seconds.

If the HMI starts polling before the NX1P2 has bound port 44818, every initial CIP request will fail with a TCP connection refused (no service on that port). The HMI driver may interpret these as timeouts and begin a retry loop. When the NX1P2 finally comes online, the HMI driver may then generate a burst of CIP requests to "catch up" — this burst can momentarily overwhelm the CIP connection pool and trigger a secondary timeout storm.

Recommended power-on sequencing:

• Configure the HMI application to wait 10–15 s after boot before initiating the first CIP poll (most Wecon firmware versions expose a "Link-Up Delay" or "Startup Wait" parameter)
• Enable a "Connection Retry on Error" parameter in the Wecon driver with exponential back-off, starting at 2 s and capped at 30 s
• Disable any "Auto-Reconnect Burst" or "Reconnect on Power-On" feature that opens all connections simultaneously when the PLC becomes reachable
• Use the NX1P2's _Card1Running system-defined variable (or equivalent) as a precondition flag read by the HMI to confirm the PLC is in RUN mode before initiating normal polling

8. W4S1-05D Switch Behavior in an EtherNet/IP Cell

The W4S1-05D is an unmanaged 5-port industrial Ethernet switch rated for 10/100 Mbps operation. Behavioral characteristics relevant to EtherNet/IP troubleshooting:

For a 2-HMI + 1-PLC topology, the W4S1-05D is functionally adequate at the physical and data link layers. Issues that can still arise:

1. Duplicate IP addresses: Two devices configured to the same IP cause the switch's MAC table to flip-flop between the two MACs. Verify unique IPs with a laptop temporarily connected to the switch.
2. Auto-negotiation mismatch: If a device is hard-set to 100 Mbps/full-duplex while the switch is auto-negotiating, the device may fall back to half-duplex, producing late collisions that the EtherNet/IP driver interprets as timeouts. Force both ends to the same speed/duplex.
3. Broadcast storms: An HMI in a misconfigured state may broadcast ARP requests in a tight loop. The unmanaged switch propagates these to every port. The only mitigation is to identify and disconnect the offending device.
4. Port-to-port latency: While 10 µs per frame is negligible, store-and-forward means the switch must receive the entire frame before forwarding. With many small CIP packets at high rates, the queue depth on each egress port grows and contributes to jitter.
5. Default gateway configuration: The W4S1-05D is a Layer 2 switch and does not require a default gateway for local traffic. Configuring an IP address on the switch (for management, if any) does not affect frame forwarding. The HMI should be configured with the NX1P2's IP as a directly reachable host — no default gateway is needed for a flat subnet.

For deeper diagnostics, temporarily replace the W4S1-05D with a managed switch (e.g., W4S1-03B, Cisco IE-3300, or Hirschmann RS20) that supports port mirroring. This allows a Wireshark capture of in-flight EtherNet/IP traffic without disrupting the network.

9. Sysmac Studio Diagnostic Counters and Event Log

Sysmac Studio provides live diagnostic counters on the NX1P2 EtherNet/IP port. Open the controller online and navigate to Communications Setup → Built-in EtherNet/IP Port → Connection Information. The following counters are available:

The Sysmac Studio event log (Controller → Events) categorizes errors with codes; EtherNet/IP-related codes fall into the ranges documented in the NJ/NX-series Troubleshooting Manual (W503):

If event codes in the 0x04A0 or 0x04A1 range appear, the NX1P2 has hit its TCP socket or CIP connection ceiling — this is the smoking gun for connection-pool exhaustion and confirms the root cause.

For deeper visibility, enable the NX1P2's SD Memory Card Event Logging (or syslog server) to capture the event log continuously across the boot window and during peak HMI activity. Event logs retrieved only when Sysmac Studio is connected can miss transient conditions that occur between online sessions.

10. Wireshark Capture Methodology

When the W4S1-05D is swapped for a managed switch with port mirroring, the following Wireshark filters isolate EtherNet/IP traffic for analysis:

# All CIP traffic between HMI and PLC
ip.addr == 192.168.1.20 && ip.addr == 192.168.1.10 && cip

# Only CIP explicit messaging service requests
cip.cm.service == 0x4C || cip.cm.service == 0x4D || cip.cm.service == 0x4E

# TCP connection establishment failures (SYN without SYN-ACK)
tcp.flags.syn == 1 && tcp.flags.ack == 0 && !tcp.analysis.successful

# TCP retransmissions indicating packet loss
tcp.analysis.retransmission

# Filter by Wecon HMI vendor (OUI may vary by model)
eth.addr[0:3] == <wecon-OUI-bytes>

Key observations to make in the capture:

• Burst patterns: Look for a sudden spike of CIP requests at HMI boot or after a screen change. This indicates an aggressive refresh interval or a missed-response cascade.
• CIP error responses: A response with General Status = 0x01 (Resource unavailable) or 0x02 (Invalid parameter) indicates the NX1P2 is rejecting requests due to connection-pool or scan-time exhaustion.
• TCP RST packets: A RST sent by the NX1P2 to the HMI indicates the CPU closed the connection. Repeated RSTs on the same connection confirm exhaustion, not a transient network issue.
• Inter-request spacing: The delta between consecutive CIP requests from a single tag should match the configured refresh rate. If the actual delta is significantly larger, the NX1P2 is falling behind.

11. Step-by-Step Resolution Procedure

Apply the following sequence in order. Each step should be verified before moving to the next.

1. Confirm NX1P2 firmware version. In Sysmac Studio: Controller → Online → CPU/Expansion Racks Information. Update to the latest NX1P2 firmware from the official Omron support portal. Earlier NX1P2 firmware revisions had known EtherNet/IP connection-handling bugs that improved significantly in later revisions.
2. Verify Wecon HMI firmware version. In the Wecon configuration software: System Settings → About. Update to the latest Wecon firmware; older versions have known EtherNet/IP driver bugs that produced spurious timeouts. Check the Wecon release notes for "CIP connection leak" or "timeout" entries.
3. Capture baseline event log. In Sysmac Studio: Controller → Events → Save to File. Note any EtherNet/IP (0x03CE) or TCP/IP (0x04A0, 0x04A1) error codes.
4. Audit the CIP connection count. Disconnect both HMIs, connect Sysmac Studio, and read the CIP Server Connections counter — it should drop to the Studio's own connection count (typically 2–4). Reconnect HMI #1 only; the counter should rise by the HMI's connection count (typically 4–12). Reconnect HMI #2; the counter should rise by the second HMI's connection count. If the counter approaches or exceeds the NX1P2's connection budget, reduce connection usage per HMI in step 6.
5. Increase HMI tag refresh interval. In the Wecon software, open each tag's properties. Change the refresh rate from the default (typically 1000 ms) to 2000 ms for status tags, 5000 ms for diagnostic tags, and 10000 ms for read-only reference values. Critical control tags (estop, run command, fault reset) can remain at 200–500 ms; these are typically a small subset.
6. Group tags into arrays. In Sysmac Studio, define a structure containing related tags and read the structure as a single CIP request rather than reading each member individually. Wecon supports reading tags by symbolic path; reference the NX1P2 tag structure name.
7. Enable HMI link-up delay and retry logic. In the Wecon software: Communication Settings → Driver Parameters. Set the connect-wait time to 10–15 s, the retry count to 10, and enable exponential back-off. Disable any auto-reconnect burst feature.
8. Hard-set Ethernet speed and duplex on HMIs and NX1P2. Wecon software: Communication Settings → Ethernet → Speed/Duplex → 100 Mbps / Full. Sysmac Studio: Built-in EtherNet/IP Port → Link Settings → 100 Mbps / Full. This eliminates auto-negotiation mismatches with the W4S1-05D.
9. Verify unique IP addresses. From a laptop connected to the W4S1-05D, run arp -a and ping each device. Confirm each device has a unique MAC-to-IP mapping. Resolve any duplicate IPs immediately.
10. Reduce active connections per HMI. Some Wecon firmware versions open a separate CIP connection per screen. Combine screens into a single tag group where possible, or disable polling on screens not currently displayed (Wecon's "Screen Active Polling" feature).
11. Capture event log after 24 hours of normal operation. Reconnect Sysmac Studio and export the event log. Compare to the baseline. The number of EtherNet/IP and TCP/IP errors should drop substantially. If 0x04A0/0x04A1 codes still appear, reduce HMI connection usage further, split the network onto two switches (one HMI per switch segment), or migrate to an NX102 or NX502 controller with a larger connection budget.

12. Verification and Long-Term Stability

After applying the resolution procedure, validate with the following checks:

• Run the system for at least 24 hours under normal operating conditions, including a representative mix of screen navigation, recipe changes, and alarm acknowledgements.
• Export the NX1P2 event log and confirm zero EtherNet/IP (0x03CE) and TCP/IP socket (0x04A0/0x04A1) error events during the validation window.
• In Sysmac Studio, monitor the CIP Server Connections counter during peak screen activity (e.g., a recipe change screen with many tags); it should remain below 50% of the budget with headroom for transient bursts.
• On the Wecon HMI, navigate through every screen and confirm no timeout events appear in the HMI's system log or alarm history.
• Use a managed switch with port mirroring to capture a Wireshark trace during a screen change; verify the CIP request rate is consistent with the configured refresh interval (no burst patterns beyond the expected reconnect handshake).
• If the Wecon HMI offers a connection quality metric, confirm it stays at 100% during a full operating shift.

For deployments where the NX1P2 connection budget remains tight after optimization, consider the following:

The NX102 and NX502 also support the OPC UA server feature, which 3rd party HMIs can connect to as an alternative to CIP polling. OPC UA uses publish/subscribe rather than request/response, eliminating the timeout pattern entirely. Verify OPC UA server availability for your specific NX102/NX502 part number in the controller datasheet before specifying it as a long-term solution.

13. Troubleshooting Matrix

Frequently Asked Questions