Omron NB HMI Communication Error: PLC Cable, Port, and Settings

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An Omron NB HMI communication error usually comes down to one of four things: the wrong PLC driver, the wrong COM port, a cable that does not match the selected electrical interface, or communication parameters that differ between the HMI and PLC.

The message on the screen may say PLC No Response, but that does not automatically mean the PLC has failed. An NB panel can download a project normally over USB while its PLC cable is connected to the wrong port. It can also ping an Ethernet PLC while using the wrong protocol or FINS node settings.

This guide focuses on the standard Omron NB Series and NB Series (-V1) panels programmed with NB-Designer, including NB3Q, NB5Q, NB7W, and NB10W models. The NB-S series has its own user manual and connection restrictions. Always confirm the complete HMI model and PLC model before applying a cable diagram or port setting.

What Does the Omron NB Communication Message Mean?

For a serial connection, an NB panel may display a message such as:

PLC No Response: 00-01-01

Omron explains this format as:

PT number – PLC station number – PT serial port number

In the example above, PT No. 0 has lost communication with PLC station 1 through COM1. Port suffix 01 represents COM1 and 02 represents COM2.

For Omron Ethernet UDP drivers, the same style of message identifies the PT, PLC node, and port information used by that connection. Read it with the driver type in mind rather than assuming every number has the same meaning on serial and Ethernet projects.

There is also an important difference between these two messages:

PLC No Response: The NB did not receive a reply. Look first at the cable or network path, selected port, station or node, protocol, and PLC communication service.
PLC Response Error: The PLC returned an abnormal response to an HMI read or write request. The link may be working, but an address, command, driver, access condition, or FINS conversion setting is wrong.

Record the full message before restarting the panel. A photograph of the error, HMI nameplate, PLC model, and cable ends is usually more useful than the statement “the HMI will not connect.”

Quick Reference: Symptoms and First Checks

Symptom	Likely area	First check
PLC No Response: 00-01-01	COM1 link to PLC station 1	COM1 assignment, station number, cable, serial parameters
Error suffix ends in 02	COM2 connection	Whether the HMI model has COM2 and the cable uses the COM2 pinout
Project downloads over USB, but PLC data is blank	PLC host connection is separate from project transfer	PLC driver, communication port, and PLC cable
PLC Response Error	PLC replied with an abnormal result	Driver, device address, data range, read/write permission
Ethernet link is on but no PLC data updates	Protocol or application setting	HMI driver, PLC IP, UDP/TCP port, node ID, PLC service
Only one screen produces the error	Invalid object or address	Addresses, data lengths, macros, alarms, and background objects
Communication is slow after opening a screen	Polling load or retries	Discontinuous addresses, logging, macros, timers, and baud rate
Communication drops when a motor or contactor operates	Noise or cable routing	Shielding, grounding, separation from power wiring
Error starts after replacing the HMI	Model or port mismatch	Full suffix, COM1/COM2 capability, Ethernet option, downloaded project

Safety Before Handling HMI or PLC Cables

The NB serial ports are not intended for hot plugging. Before disconnecting a D-sub connector, rewiring RS-422A/RS-485 terminals, or moving a communication cable inside a panel:

Stop the machine in a controlled condition.
Follow the site’s lockout and electrical-safety procedure.
Isolate the relevant power sources.
Confirm that hazardous voltage is absent before touching conductors.
Back up the NB-Designer project and PLC program.

Omron also instructs users to keep communication connector screws tightened. Avoid placing cable weight or door movement on the HMI connector.

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Step 1: Identify the Exact NB Model and Port

The port arrangement is not the same across the NB family. This is one of the main reasons a cable that worked on an NB7W does not work when moved to an NB3Q.

NB model family	COM1	COM2	Ethernet
NB3Q	RS-232C/RS-422A/RS-485, one mode at a time	Not fitted	Available on TW01B and TW01B-V1 models
NB5Q	RS-232C	RS-232C/RS-422A/RS-485, one mode at a time	Available on TW01B and TW01B-V1 models
NB7W	RS-232C	RS-232C/RS-422A/RS-485, one mode at a time	Available on TW01B and TW01B-V1 models
NB10W	RS-232C	RS-232C/RS-422A/RS-485, one mode at a time	Fitted on the listed TW01B and TW01B-V1 models

The serial interfaces are non-isolated. Omron specifies a maximum transmission distance of 15 m for RS-232C and 500 m for RS-422A/RS-485, subject to the connection method and cable requirements in the manuals.

The point that matters in practice is simpler:

NB3Q has only COM1. Its COM1 combines RS-232C, RS-422A, and RS-485 pins.
NB5Q, NB7W, and NB10W use COM1 for RS-232C and COM2 for the multi-interface serial connection.

The Host Connection Manual warns that cable diagrams marked for COM2 on NB5Q/NB7W/NB10W must not be copied blindly to the NB3Q COM1 connector. Check the NB3Q pin definitions separately.

Also check the model suffix before troubleshooting Ethernet. A TW00B or TW00B-V1 NB3Q, NB5Q, or NB7W does not have the Ethernet interface found on the corresponding TW01B model.

Step 2: Check the PLC Driver and Network Configuration in NB-Designer

Open the project in NB-Designer and inspect the Configuration and Setup Window. The drawn network should match the equipment physically connected to the HMI.

Check each PT and PLC object for:

Exact controller manufacturer and family
Communication protocol
HMI port or network interface
Master/slave role where applicable
PLC station or node number
Baud rate and serial frame format
HMI and PLC IP addresses
UDP or TCP port number

The correct manufacturer name is not enough. Omron CP Series Ethernet UDP, Omron CJ/CS/NJ Series Ethernet UDP, Omron NX Series Ethernet UDP, Omron Host Link, Modbus RTU, Modbus ASCII, and Modbus TCP are different drivers.

For example, a CP1L with built-in Ethernet must be configured with the supported CP Series Ethernet driver, not simply left on the project’s default CJ/CS/NJ driver. A protocol mismatch can stop compilation or produce a panel that never receives usable PLC data.

One physical COM port cannot run multiple communication systems at the same time. If two host objects are assigned to COM1, fix the network design instead of increasing the timeout.

After correcting the project, compile it and review every warning before downloading. Keep the edited NB-Designer file as the new master copy; otherwise the next service download may restore the bad settings.

Step 3: Verify the PLC Cable, Not Just the Connector

A D-sub 9-pin plug is a connector shape, not a communication standard. The cable must match:

The exact NB model
COM1 or COM2
RS-232C, RS-422A, or RS-485
The PLC CPU or communication module
The selected protocol
Any required adapter or termination

Omron lists the following standard NB-to-PLC accessories:

XW2Z-200T: 2 m RS-232C cable for supported CP/CJ/CS PLC connections
XW2Z-500T: 5 m RS-232C cable for supported CP/CJ/CS PLC connections
NB-RSEXT-2M: 2 m cable for supported RS-422A/RS-485 connections

These part numbers are not universal for every PLC or third-party controller. Use the Host Connection Manual chapter for the selected driver to confirm the complete system configuration and wiring diagram.

Why COM1 and COM2 cables are not interchangeable

Omron explicitly warns that COM1 and COM2 communication cables are not interchangeable. The pin functions differ, even though both connectors may be D-sub 9-pin.

For a user-built cable, check every conductor end to end. Look for:

Transmit and receive pins crossed correctly for RS-232C
Signal ground connected as specified
Correct RS-422A transmit and receive pairs
Correct RS-485 polarity
Connector gender and pin numbering viewed from the correct side
Loose crimp contacts or false solder joints
Shield and termination installed as shown in the manual
Connector screws fully secured

Do not match terminals only by labels such as A and B. Manufacturers do not always use those labels with the same polarity convention.

If a machine is down and the original cable identity is uncertain, Kwoco can help match an Omron NB cable, HMI, PLC option board, or replacement unit. Send the complete HMI and PLC model numbers, clear photos of both connectors, the port being used, and the NB-Designer protocol setting. That is enough to avoid most connector-only guesses.

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Step 4: Fix Omron Host Link Serial Communication

For an Omron CP, CJ, or CS PLC connected by Host Link, both devices must use the same serial format and speed, and the PLC port must actually be set for Host Link.

The NB Series Setup Manual gives the following Host Link communication settings:

Parameter	Host Link setting
Data bits	7
Stop bits	2
Parity	Even
Baud rate	Any supported value, but HMI and PLC must match
Unit/station number	00 in the documented basic setup

Do not apply this 7-E-2 format to Modbus or a third-party serial driver. It is the Omron Host Link setting described in the NB setup procedure.

In the PLC project, verify:

The physical PLC port being used
Host Link mode rather than Toolbus, no-protocol, or another serial mode
Baud rate
Data bits, parity, and stop bits
Unit number
Option-board or serial-module settings
DIP switch settings that determine whether PLC Setup values are active

On CP1L and CP1H models, port 1 and port 2 use different PLC Setup words and may be controlled by front DIP switches. Read the current PLC configuration instead of copying values from another machine.

For CP1E and CP2E models, check the exact CPU and serial option. Omron states that an NB cannot connect to the CP2E built-in two-wire RS-485 port using the Host Link arrangement documented in the setup manual. Use a supported connection method and hardware combination.

Host Link over RS-422A

Omron’s NB connection guidance uses four-wire RS-422A when extending Host Link distance. Do not assume a two-wire RS-485 port can replace it because both use differential signaling.

Verify the send and receive pairs at both ends, along with termination and signal ground. If communication works at low speed on the bench but fails after installation, inspect cable route, shielding, and topology before raising the baud rate.

Step 5: Fix Ethernet Communication

Ethernet troubleshooting should be divided into network reachability and PLC protocol communication.

Check the live IP settings

Confirm the actual values in the NB project, the NB System Setting Mode, and the PLC project:

HMI IP address
PLC IP address
Subnet mask
Default gateway, if routing is used
UDP or TCP port
Omron FINS network and node number where applicable

For a simple local connection, the HMI and PLC normally need addresses in the same IP subnet and each device must have a unique IP address. When routers are used, verify the gateway and route rather than changing the subnet mask until communication appears.

Models with Ethernet use 10/100BASE-T. Check the RJ45 link indicators, switch power, cable latches, and switch port. Test with a known-good standard Ethernet cable and, where permitted, a simple isolated HMI-to-PLC network.

Match the protocol and port

A successful ping shows that IP packets can reach the PLC. It does not prove that the PLC is listening for the protocol selected in NB-Designer.

For Omron Ethernet UDP connections, the V107 Setup Manual shows the HMI and PLC registered in PT Property > PT > Communication Setting, with matching IP, port, and protocol entries. Its FINS/UDP examples use port 9600, but other protocols have different ports. Do not apply 9600 to Modbus TCP or a third-party PLC without its connection manual.

Check that:

The NB driver matches the PLC family.
The PLC-side Ethernet or FINS/UDP settings are enabled.
The HMI targets the PLC’s actual IP address.
HMI and PLC port numbers agree.
FINS network and node numbers are valid and unique.
A managed switch, VLAN, firewall, or router is not blocking the traffic.

Check FINS node and IP conversion settings

An Omron Ethernet link can be physically healthy but still fail because its FINS addressing is inconsistent.

The network number identifies the FINS network; it is not the same thing as the IP subnet. The node ID identifies the device in that FINS network and must not conflict with another node.

For projects using an IP address table or combined IP/FINS conversion, verify that the NB’s own node ID has not been entered as a remote PLC entry. Omron documents this as one condition that can produce PLC Response Error.

If the error is PLC No Response, trace the PT number, PLC node, and port information shown in the message. If it is PLC Response Error, inspect the returned request: the PLC may be reachable but rejecting an address or command.

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Step 6: Use NB-Designer Direct Online Test

Omron recommends Direct Online Test to separate parameter problems from the physical NB-to-PLC cable.

The practical sequence is:

Back up the HMI and PLC projects.
Connect the engineering PC to the PLC using the correct PLC programming cable or network path.
Confirm that PLC programming software can go online.
Exit the PLC program-transfer mode.
In NB-Designer, select Tools > Direct Online Test.
Observe whether the test project can read the configured PLC data.

If Direct Online Test fails, compare the NB project driver and communication parameters with the PLC configuration.

If Direct Online Test works but the physical NB does not, focus on the HMI port selection, NB-to-PLC cable, connector pinout, and HMI serial or Ethernet hardware.

This test is far more useful than changing several parameters at once because it removes one part of the path without changing the PLC program.

Step 7: Check Whether Every Screen Fails

All objects have stopped updating

When all PLC values are stale, investigate the shared connection:

PLC power and CPU mode
Driver and host selection
COM1/COM2 or Ethernet interface
Cable and switch
Baud rate or IP settings
PLC communication service
Station or node number

Only one screen causes the message

The physical link is probably working. Inspect the objects on that screen for:

Unsupported or out-of-range PLC addresses
A 32-bit value crossing an invalid word boundary
Incorrect array length
Read-only or write-protected devices
Indirect addresses
Macros that access PLC memory
Alarm, event, recipe, or trend objects

An invalid read/write request can produce PLC Response Error even while other screens work normally.

The message appears everywhere, but most values work

Look for a background object. Data logs, alarms, event monitoring, PLC Control objects, timers, macros, common sheets, and data history can keep polling a bad address on every screen.

Use a copy of the project to disable suspect groups methodically. Do not tear apart the only working copy.

Step 8: Fix Slow or Intermittent Communication

Slow page changes are often caused by polling load rather than a defective HMI.

Omron lists these common contributors:

Too many PLC-linked objects on one screen
Large numbers of discontinuous addresses
Macros that repeatedly access PLC addresses
Too many timers on common sheets
Continuous Data Log, XY Graph, or Data History tasks
Large alarm and event tables with scattered addresses
Too many PLC Control objects
Too many connected controllers and communication addresses
On-site electrical interference

Group PLC addresses where the control design permits it and lengthen sampling intervals for background functions that do not need fast updates. A larger timeout is not a substitute for reducing unnecessary requests.

If communication drops when an inverter, servo, contactor, or solenoid operates, inspect the installation:

Keep communication cable away from power and motor wiring.
Use the shielded cable and grounding method specified by Omron and the PLC manufacturer.
Check protective-earth and cabinet bonding.
Inspect cable damage near hinges and moving machine sections.
Check RS-422A/RS-485 termination and topology.

Omron’s troubleshooting guide recommends keeping the communication cable at least 10 cm from power lines. Greater separation may be required by the equipment manuals or site EMC standard.

Step 9: Build a Minimal Test Project

A small test project quickly shows whether the fault belongs to the connection or the application.

Select the exact NB model and suffix.
Add one PLC with the correct driver.
Assign it to the actual COM port or Ethernet interface.
Enter the verified PLC parameters.
Add one read-only display for a known valid, stable PLC word.
Compile and run Direct Online Test.
Download the test project to the HMI only after backing up the production project.

If the minimal project fails in Direct Online Test, revisit the driver and PLC-side settings.

If it passes online but fails on the HMI, revisit the cable, HMI port, and hardware.

If it works on the HMI, the original project’s addresses, macros, background functions, or communication load need to be isolated.

Communication Problems After Replacing an NB HMI or PLC

Do not select a replacement by screen size alone. Before transferring the project, record:

Complete NB model, including TW00B, TW01B, and -V1 suffixes
Display size and resolution
Supply and mounting details
COM1 and COM2 use
RS-232C, RS-422A, or RS-485 interface
Ethernet requirement
NB-Designer project and software version
PLC model, option board, and firmware
Cable part number or verified pinout
PLC serial or Ethernet settings

After replacing a PLC, restore its communication parameters as well as the ladder program. A PLC with correct machine logic but a default serial port will still produce PLC No Response.

After replacing an HMI, download the correct model project and verify the port assignment before connecting the PLC cable. A project converted to another NB model can retain communication assumptions that no longer match the rear connectors.

Kwoco can help check a replacement Omron NB HMI, PLC, cable, or communication option against these details. For discontinued or mixed-generation equipment, include the original project version and photographs of the rear ports so electrical compatibility is checked before installation.

Frequently Asked Questions

What does PLC No Response: 00-01-01 mean on an Omron NB HMI?

It means PT No. 0 has lost serial communication with PLC station 1 through COM1. Verify the COM1 assignment, PLC station number, cable pinout, serial format, and PLC port mode. A suffix ending in 02 points to COM2.

Should I connect the PLC to COM1 or COM2 on an Omron NB HMI?

It depends on the HMI model and interface. NB3Q has only COM1, which supports one selected RS-232C/RS-422A/RS-485 mode. On NB5Q, NB7W, and NB10W, COM1 is RS-232C and COM2 is the multi-interface RS-232C/RS-422A/RS-485 port.

Can I use a normal straight-through RS-232 cable between an NB HMI and PLC?

Not safely as a general rule. The cable must follow the Omron Host Connection Manual for the exact HMI port and PLC. For supported CP/CJ/CS RS-232C connections, Omron lists XW2Z-200T and XW2Z-500T; other PLCs and ports may require different wiring.

Why can I download the NB project but still get PLC No Response?

Project transfer and PLC communication are separate paths. USB or Ethernet may download the application correctly while the project uses the wrong PLC driver, COM port, station, IP address, protocol port, or physical PLC cable.

Why can the NB HMI ping the PLC but not read PLC data?

Ping confirms IP reachability, not the PLC protocol. Check the NB-Designer driver, PLC IP and port, FINS network and node settings, PLC-side Ethernet service, and requested device addresses. A reachable PLC can still reject an unsupported read or write request.

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When an HMI Port Is Actually Faulty

Suspect the NB hardware only after configuration and external components have been isolated.

A serial port becomes a credible suspect when:

The exact driver and communication parameters are verified.
The PLC port communicates with another device.
A known-good cable with the correct pinout is used.
Direct Online Test succeeds with the same project settings.
The NB still sends no valid data or receives nothing on the selected port.

An Ethernet port becomes suspect when it cannot establish a link with multiple known-good cables and switch ports, while the correct Ethernet-capable NB model is being used.

Before replacement, inspect the D-sub connector for bent pins, loose mounting, cable strain, and evidence of hot-plug damage. Keep the production project backup with the machine.

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