Weintek HMI "PLC No Response" Error: Serial and Ethernet Fixes

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The Weintek HMI "PLC No Response" message means the HMI did not receive a valid reply to at least one device request within the configured time. It does not always mean that the PLC is offline.

If every PLC value has stopped updating, the problem is likely in the communication path or device settings. If most values still work, one bad register, missing tag, wrong station number, or background object may be enough to trigger the same message.

That distinction should guide the repair. Replacing a cable will not correct an invalid address, and increasing the timeout will not repair reversed RS-485 wiring.

This guide applies to Weintek HMI projects created in EasyBuilder Pro, including common cMT, cMT X, iE, XE, and related series. Available diagnostic tools and network interfaces vary by model, so confirm the exact HMI model, EasyBuilder Pro version, selected PLC driver, and PLC connection guide before making changes.

What “PLC No Response” Actually Means

In EasyBuilder Pro, Window No. 5 is the default Device No Response system message window. The software opens it when communication with a configured device remains disconnected longer than the device’s Timeout setting.

Window No. 5 is only the visible warning. The underlying cause can be:

No physical connection to the PLC
Incorrect serial parameters
Wrong serial station or Modbus slave number
Incorrect cable pinout or RS-485 polarity
Wrong HMI, PLC, or project IP address
Wrong Ethernet protocol port
A PLC protocol server that is disabled or restricted
An invalid register, unsupported address, or missing symbolic tag
A global alarm, data-sampling item, macro, or transfer object polling a bad address
Communication noise, excessive network delay, or a busy controller

Weintek’s current troubleshooting guidance describes the message as a generic communication error. One failed value request can produce it even while other PLC data continues to update.

Read the Symptom Before Changing Settings

The fastest diagnosis starts with where and when the popup appears.

What you observe	Most likely area	First action
No PLC data works on any page	Physical link, driver, COM/IP settings, PLC protocol	Check link and device configuration
Error appears only on one HMI page	Local object or address on that page	Inspect objects on the affected window
Error appears on every page, but most live data still works	Global object or one background request	Check alarms, sampling, macros, transfers, and schedulers
Error began after a PLC program download	Tag or register mapping changed	Re-export/import tags and verify addresses
Error occurs when a motor or contactor switches	Serial noise, grounding, shielding, or cable route	Inspect separation, shield, earth, and termination
Ethernet link is present but no PLC data works	IP, subnet, port, protocol, permissions, or driver	Compare all three IP settings and the connection guide
Popup disappears by itself after a few seconds	Intermittent or delayed response	Use the Diagnoser before increasing timeout

Record the HMI model, PLC model, EasyBuilder Pro version, driver name, interface, and exact operating condition. Save a copy of the HMI and PLC projects before testing.

Five-Minute Checks That Often Find the Fault

Before opening every parameter dialog, check these basics:

Is the PLC powered, running, and free of its own communication or CPU fault?
Does the HMI use the intended COM or LAN port?
Is the selected EasyBuilder Pro driver correct for the PLC and protocol?
Does the project point to the actual station number or IP address?
Is the cable connected to the port shown in the Weintek PLC connection guide?
Did the problem begin after a cable, PLC, HMI, switch, or project change?
Does a known-good value still update?

If one known value works, avoid changing global communication parameters immediately. Find the request that fails.

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Serial Fixes for RS-232 and RS-485 Connections

Serial communication is unforgiving. Baud rate, data format, station number, interface type, and wiring must all agree.

1. Confirm the driver and COM interface

In EasyBuilder Pro, open:

Home > System Parameters > Device

Select the PLC device and verify the exact driver name. Similar PLC families may have separate drivers for programming-port protocol, Modbus RTU, Host Link, MPI, or a vendor-specific serial protocol.

Then confirm the interface:

RS-232
RS-485 2-wire
RS-485 4-wire

Selecting RS-485 2-wire in the project while using an RS-232 pinout will never work, even if the baud rate and station are correct.

Also confirm that the physical socket supports the selected interface. A DB9 connector is only a connector shape; it does not prove that the electrical interface or pinout is the one expected.

2. Match all serial communication parameters

The following values must match at both ends:

Baud rate
Data bits
Parity
Stop bits

A typical mismatch does not always produce complete silence. It may cause checksum errors, intermittent values, or communication that works at a low polling load and fails when more objects are displayed.

Read the settings from the PLC software or PLC hardware configuration. Do not assume the PLC still uses its factory default.

3. Verify the station number

The PLC station, node, unit ID, or slave number in EasyBuilder Pro must identify the actual device.

On a multi-drop RS-485 network:

Every slave must have a unique station number.
The HMI objects must reference the intended station.
The configured device must actually exist on the bus.
A gateway may require both a gateway address and a downstream unit ID.

EasyDiagnoser error code 4 specifically means that the device using the requested station number does not exist.

4. Check the cable against the exact connection guide

Serial cable pinouts are not universal. Download the Weintek PLC connection guide for the exact driver and compare both ends wire by wire.

For RS-232, verify transmit, receive, and signal ground. TX and RX normally cross between endpoints, but the official pinout should decide the wiring.

For RS-485 2-wire, verify the differential pair. Manufacturers use labels such as A/B, D+/D-, or +/-, and the A/B convention is not applied consistently across all equipment. Use the terminal function and connection diagram rather than matching letters by habit.

For RS-485 4-wire, verify both transmit and receive pairs. A crossed pair or incorrect transmit-to-receive relationship can leave the HMI sending requests that never reach the PLC receiver.

Inspect:

Loose screw terminals
Bent DB connector pins
Broken conductors near cable glands
Incorrectly joined shield and signal ground
Cable damage in moving sections
Unapproved USB-to-serial converters used during simulation

If a pre-made cable worked previously and the settings have not changed, testing with a known-good correct cable is a sensible next step.

5. Review RS-485 topology and noise

RS-485 should be wired as a bus rather than a star unless the hardware documentation explicitly supports another topology. Long stubs, duplicated termination, missing termination, poor bonding, and routing beside motor output cables can cause intermittent no-response events.

Use the termination and biasing arrangement specified by the PLC and HMI connection guides. Do not add resistors blindly; some devices already include switchable or internal components.

Route serial communication away from:

Servo and inverter U/V/W cables
Braking-resistor wiring
Contactor and solenoid wiring
High-current power conductors

Follow the manufacturer’s shield and protective-earth instructions. If communication fails only when power equipment switches, capture that timing before replacing the HMI or PLC.

6. Treat timeout and turnaround delay as tuning parameters

EasyBuilder Pro provides Timeout and, for supported serial drivers, Turn around delay. The timeout determines how long communication can remain disconnected before Window No. 5 appears. Turnaround delay inserts an interval before the HMI sends the next command.

Do not increase these settings as the first repair. A longer timeout can hide a missing station, bad cable, or unsupported address while leaving stale data on the screen.

Adjust delay values only when:

The PLC connection guide calls for them.
The PLC needs additional processing time.
A packet trace shows valid but late replies.
Wiring, station, and data format have already been verified.

Some PLC drivers have protocol-specific timing recommendations. Use the values in the selected driver’s connection guide rather than copying a setting from another PLC brand.

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Serial Symptom Guide

Serial symptom	Likely causes	Useful check
No requests or replies	Wrong COM port, interface, driver, or dead port	Confirm project interface and physical HMI port
Requests leave HMI, no reply	Wrong station, pinout, polarity, PLC protocol disabled	Check station and official cable diagram
Checksum errors	Data-format mismatch, noise, pair fault	Compare parity/data/stop bits and inspect wiring
Works at low baud only	Cable quality, topology, termination, noise	Review RS-485 installation
Fails when a certain screen opens	Invalid address on that window	Locate the object’s request in Diagnoser
Random failures during machine motion	EMC, grounding, damaged moving cable	Correlate events with contactors, drives, or axis movement

Ethernet Fixes for Weintek HMI-to-PLC Communication

An Ethernet link light proves only that a physical link exists. It does not confirm the correct IP route, protocol port, PLC service, or tag request.

1. Compare the three IP configurations

There are three separate places to verify:

HMI runtime IP address: The address configured on the actual Weintek HMI LAN port.
PLC IP address: The address stored in the PLC or its Ethernet module.
PLC address in the HMI project: The destination configured under the device in EasyBuilder Pro.

The project destination must match the PLC. The HMI and PLC must also have compatible subnet settings for direct communication, or a valid gateway and route must exist.

Check for:

Duplicate IP addresses
Incorrect subnet masks
A stale project IP after PLC replacement
DHCP assigning an unexpected address
A gateway entered where no routed network exists
Ethernet cable connected to the wrong HMI LAN port

A laptop on the same network can help confirm addressing. However, a successful ping proves only IP reachability. The PLC protocol may still be disabled, blocked, listening on another port, or rejecting the requested access.

2. Check dual-LAN configuration

Many Weintek cMT X models provide LAN 1 and LAN 2. Weintek recommends placing the two ports on different subnets under normal dual-network use. Configuring both interfaces on the same subnet can create routing ambiguity and communication errors.

If bridge mode is intentionally enabled on a supported model, follow the model manual because the two ports then serve a different network purpose.

There is another special case: on a CODESYS-enabled Weintek HMI, the CODESYS runtime may control LAN 1 and the CAN port. The standard HMI runtime cannot use a port that has been assigned to CODESYS. Verify the HMI model, license, and network-port allocation.

3. Verify the protocol port and PLC service

The EasyBuilder Pro driver normally supplies the protocol’s standard port, but the PLC or gateway may be configured differently. Modbus TCP, for example, normally uses TCP port 502.

Confirm:

The port in EasyBuilder Pro matches the PLC or gateway.
The required server or communication service is enabled in the PLC.
PLC access control permits the HMI connection.
The selected driver matches the PLC protocol and firmware.
A firewall, managed switch ACL, VPN, or router is not blocking the port.

Vendor-specific PLCs may also require an open-connection setting, connection resource, access level, or imported tag database. The Weintek connection guide for the exact driver should be the reference.

4. Remove network middlemen for a controlled test

If the addressing looks correct, temporarily test the HMI and PLC on a simple isolated network using known-good cables and compatible static IP settings. Removing routers, unmanaged switches, wireless bridges, and remote-access paths helps separate a PLC/HMI configuration issue from the plant network.

Do not change the live plant network without authorization. Record the original settings before moving cables or assigning temporary addresses.

If direct communication works, restore one network component at a time. Then check switch port errors, VLAN membership, duplicate IPs, network loops, connector damage, and traffic loading.

5. Check tags and register access

Ethernet can be healthy while one request is invalid.

Common causes include:

A symbolic tag was renamed or deleted in the PLC.
The HMI tag database was not refreshed after a PLC change.
The requested array index is outside the declared range.
The register address is outside the PLC’s configured memory range.
The selected data type or length makes the request cross an invalid boundary.
The driver does not support reading or writing that address type.
A Modbus request exceeds the supported number of words.

After a PLC project change, export the current tags, import them into EasyBuilder Pro, compile the HMI project, and review warnings before downloading.

Why the Error Appears on Only One Screen

If the popup occurs only when a particular window opens, the communication link is probably working. Inspect every PLC-reading object on that window, including objects placed on an underlay.

Look for:

Numeric displays and inputs
Bit lamps and switches
Trend and history objects
Indirect windows
PLC control objects
Macros triggered when the window opens

An object that only writes a value may still appear normally. A read object may disappear or remain unavailable because the HMI cannot confirm its live state.

Use a copy of the project for isolation. Disable or remove suspect objects in small groups, compile, and retest. Do not dismantle the original project.

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This pattern often points to a background request.

Global objects continue polling regardless of the current page. Check:

Event alarms
Data sampling
Global data transfers
Scheduled actions
PLC Control
Global condition and action-trigger objects
Timer objects
Macros
MQTT mappings that read PLC values

One obsolete alarm tag or sample address can keep Window No. 5 appearing on every page.

Compare the HMI tags with the current PLC project. Pay particular attention to objects copied from another machine, addresses left behind after a PLC migration, and tags whose data types changed.

Use Diagnoser Instead of Guessing

For supported cMT and cMT X models, the built-in Diagnoser can monitor communication from simulation or the HMI runtime. Enable it in the EasyBuilder Pro system parameters under the remote settings, then inspect the Object and Packet views.

The Object view helps identify a value that remains at Polling…. The Packet view shows the device, station, address, request result, and failed packets. From there, trace the request back to the HMI object or background function.

Older HMI models and some drivers have different diagnostic support. Use EasyDiagnoser where the HMI and driver support it, and consult the manual for known driver limitations.

Useful EasyDiagnoser Communication Codes

Code	Official meaning	What to check
1	Device is busy	PLC load, request rate, timing
3	Device does not exist	Device configuration and physical connection
4	Requested station does not exist	Station or slave number
5	Incorrect address format	Address syntax and driver
6	Address does not support the requested read/write	Address type, access direction, PLC support
8	COM port does not exist	HMI model, selected COM port, interface
9	Incorrect IP address or unable to connect	IP, subnet, route, port, PLC service
10	Checksum error	Serial format, cable, noise
22	No reply from device	Cable/link, station/IP, protocol
23	Insufficient data received before timeout	Timing, serial format, noise, device response
251	Modbus request exceeds the supported word count	Object length and register request
252	Modbus device returned an incorrect data format	Driver, function, PLC/gateway response
253	Modbus checksum error	RTU wiring, format, and noise

The code is a direction, not a complete diagnosis. Code 22, for example, can result from a wrong station number, reversed RS-485 pair, incorrect IP, disabled PLC service, or a disconnected cable.

Build a Minimal Communication Test

When a large project makes the cause difficult to see, create a test copy:

Keep the same HMI model and one correctly selected PLC driver.
Enter the verified serial or Ethernet settings.
Add one read-only object for a known valid, stable PLC value.
Run online simulation where the driver supports it, or download the test project to the HMI.
Confirm the value updates before adding more addresses.

If the minimal project fails, focus on the physical link, PLC protocol, and device settings.

If it works, the original project’s tags, objects, or polling load deserve attention. Add object groups back methodically until the failing request returns.

Should You Disable Window No. 5?

EasyBuilder Pro allows the Device No Response window to be controlled by system registers, and its displayed text can be edited. That does not make suppression a repair.

Deleting or permanently hiding Window No. 5 can leave operators looking at stale data without a clear communication warning. Resolve the fault first.

Suppression may be appropriate only when the machine design intentionally permits a device to be offline and the HMI provides another clear, validated indication of data quality and connection state. Document that behavior in the control design.

Similarly, increasing Timeout may reduce nuisance popups but can delay notification of a real failure. Make that change only after confirming the device is replying correctly but needs more time.

Frequently Asked Questions

Why does "PLC No Response" appear only on one Weintek HMI screen?

The communication link is probably working, but an object on that screen is requesting an invalid or unsupported address. Check all PLC-reading objects, underlays, window macros, indirect windows, data types, and tag names associated with the affected page.

Why can I ping the PLC but EasyBuilder Pro still shows "PLC No Response"?

Ping confirms basic IP reachability, not the PLC application protocol. Verify the EasyBuilder Pro driver, PLC destination IP, protocol port, PLC communication service, access permissions, symbolic tags, and requested addresses.

Which serial settings must match between a Weintek HMI and PLC?

The baud rate, data bits, parity, stop bits, interface type, and station number must match the PLC configuration. The cable must also follow the exact Weintek connection guide for the selected driver and HMI port.

Will increasing the timeout or hiding Window No. 5 fix the error?

No. Those changes can delay or conceal the warning without restoring communication. Adjust timeout only after diagnostics prove the device sends valid but late replies, and suppress the window only when an intentional offline state is handled safely elsewhere in the HMI design.

How can I find the exact tag or object causing Device No Response?

Use the cMT/cMT X Diagnoser or supported EasyDiagnoser tool to inspect objects and failed packets. A value stuck at Polling…, a red failed packet, its station/address, and the associated window or object ID usually identify the request that needs correction.

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When Hardware Replacement Is Justified

Replace hardware only after the external causes have been isolated.

An HMI serial port becomes suspect when the driver, parameters, station, cable pinout, and PLC port have all been verified, but a known-good device still receives no valid HMI request from that port. An Ethernet port becomes suspect when it has no link with multiple known-good cables and switch ports under the correct hardware settings.

Before ordering a replacement, record:

Full Weintek HMI model
Supply voltage and power connector
EasyBuilder Pro project version
PLC model and firmware
Selected driver and protocol
COM interface or LAN-port assignment
Cable part number or complete pinout
HMI project backup

Kwoco can help check a replacement Weintek HMI, communication cable, or PLC-side component against these details. For older panels, send photos of the HMI nameplate, power connector, rear communication ports, and existing cable ends. A similar screen size does not guarantee the same ports, project conversion behavior, or mounting cutout.

Official Weintek References

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