Pro-face HMI Communication Error with PLC: Step-by-Step Checks

Step 5: Troubleshoot Serial Communication

Errors RHAA067 through RHAA070 are commonly associated with RS-232C, RS-422, or RS-485 communication.

Confirm the serial interface

Verify that the selected HMI port supports the configured SIO type:

• RS-232C
• RS-422
• RS-485 2-wire
• RS-485 4-wire

Port capabilities differ between Pro-face models. A connector’s shape does not define its electrical interface. Some models support only one communication type on a particular COM port.

Pro-face warns that operation is not guaranteed if the project specifies a communication type unsupported by the display’s serial interface.

Match all communication parameters

Compare the HMI and PLC:

• Baud rate
• Data length
• Parity
• Stop bits
• Flow control
• Station, unit, or node number

RHAA006 and RHAA007 point toward parity or framing problems. Mismatched data format is one cause, but electrical noise and loose connectors can produce the same symptom.

If the PLC has DIP switches or rotary switches for serial settings, read their actual position. Do not rely only on an old electrical drawing.

Use the exact cable diagram

Serial pinouts are driver- and model-specific. Check the Device/PLC Connection Manual for the exact combination of:

• Pro-face HMI model and COM port
• PLC CPU or communication module
• RS-232C, RS-422, or RS-485 interface
• Required Pro-face conversion adapter
• Cable wiring and maximum length

Inspect TX/RX crossing for RS-232C, differential pairs for RS-422/485, signal ground, shield, termination, and any control signals required by the driver.

Do not match A to A or B to B without checking the functional polarity. Equipment manufacturers do not always use A/B labels consistently.

Check station addressing

On a multi-drop serial network, every PLC or controller must have a unique station number. The station selected by the HMI object or driver must exist.

If initial communication times out but wiring and data format look correct, verify:

• PLC station number
• HMI target station
• Gateway or link-unit station
• Multi-link settings
• Duplicate stations

Look for noise and topology problems

If communication fails when a contactor, inverter, servo, or solenoid operates, inspect EMC conditions:

• Separate communication cables from motor and power wiring.
• Check shield termination against the hardware manuals.
• Verify cabinet bonding and protective earth.
• Inspect cable damage at moving door or drag-chain points.
• Confirm the specified RS-485 termination and topology.

Do not add termination or earth connections by guesswork. Follow the Pro-face and PLC wiring diagrams.

Step 6: Troubleshoot Ethernet Communication

Errors RHAA065 and RHAA066 are the main Ethernet connection indicators in this context.

Check all IP addresses

Verify:

1. The HMI’s actual IP address and subnet mask
2. The PLC or communication module’s actual IP address
3. The PLC target IP stored in GP-Pro EX

Also check:

• Duplicate IP addresses
• Incorrect gateway
• Wrong network interface
• DHCP assigning an unexpected address
• PLC replacement with a default IP
• A project copied from another machine

From a PC on the same network, ping both the HMI and PLC. Pro-face recommends this as part of the RHAA065/066 diagnosis.

A successful ping proves IP reachability, not PLC protocol operation. The port, PLC communication service, connection resources, and access settings still need verification.

Verify the protocol port

The HMI destination port must match the PLC driver and PLC-side service. Do not assume that every Ethernet PLC uses the same port.

Review:

• GP-Pro EX Device/PLC port setting
• PLC or Ethernet-module open-connection setting
• TCP versus UDP
• PLC server or protocol enable setting
• Available connection resources
• Firewall or managed-switch rules

The Pro-face connection manual notes that the HMI system initially uses local ports 8000 through 8019. Avoid assigning those as HMI-side communication ports unless the current system configuration has been deliberately changed and verified.

RHAA010 and RHAA012 indicate port overlap conditions. RHAA011 means an established connection was closed, often after a PLC reset or network interruption.

Simplify the network

If settings appear correct:

1. Save the original network configuration.
2. Put a service PC, HMI, and PLC on a controlled test network.
3. Use known-good Ethernet cables.
4. Remove unnecessary routers, wireless bridges, and switches from the test path.
5. Ping both devices.
6. Test the PLC protocol.

Pro-face specifically recommends trying another hub and cable. If direct communication works, restore network components one at a time and check VLANs, switch errors, IP conflicts, routing, and port security.

Step 7: Resolve PLC-Returned and Address Errors

Codes RHAA033 through RHAA035 mean the PLC returned an error to an initial, read, or write request. The decimal and hexadecimal detail is produced by the connected device. Decode it with the PLC manual and the Pro-face driver manual.

Do not replace the HMI because a PLC rejected an unsupported request.

Out-of-range addresses

RHAA036 and RHAA037 mean a requested read or write address is outside the valid range.

Check:

• PLC CPU memory range
• Driver-supported address range
• File, bank, or block number
• Array and string length
• Recipe or data-transfer span
• Indirect address calculation
• Addresses copied from another PLC model

An object can start at a valid address and still cross beyond the valid range because its data length is too large.

Read-only and write-only addresses

RHAA038 means the HMI tried to read a write-only address. RHAA039 means it tried to write to a read-only address.

Review Data Displays, switches, input-enabled objects, triggers, and D-Scripts. An HMI object may perform both a read and a write even if its intended use appears one-directional.

Indirect and block addressing

Codes RHAA049 through RHAA054 identify unknown indirect devices, block ranges that exceed the supported area, or read/write access violations detected by the protocol driver.

Check the calculated device code, base address, offset, and complete data length at runtime. A correct design value can become invalid if the PLC writes an unexpected index.

Step 8: Use Cross Reference and Peripheral List

GP-Pro EX includes two tools that save a great deal of searching.

Cross Reference

Open:

Project > Utility > Cross Reference

Select All as the target. Search the device address shown in the error and review every part, script, alarm, sample, and trigger that uses it.

For RHAA036/037, look for addresses outside the supported range.

For RHAA038, look for a read operation on a write-only address.

For RHAA039, look for a write operation on a read-only address.

Peripheral List

Open the GP-Pro EX System Settings and select Peripheral List. Review the list of Device/PLC management addresses used by functions that communicate across all screens.

This is particularly useful when the same error follows the operator from screen to screen even though normal values continue to update.