The Mitsubishi FX5U is one of the most popular compact PLCs in the MELSEC iQ-F series, and its robust communication capabilities are a major reason it dominates modern factory automation projects. Whether you need to connect to a GOT HMI, exchange data with a variable frequency drive, link multiple PLCs over Ethernet, or integrate with a SCADA system, the FX5U offers a versatile mix of built-in ports and plug-in modules. In this guide, we break down every important aspect of Mitsubishi FX5U communication — from hardware interfaces and supported protocols to programming tips and real-world troubleshooting.
Overview of the Mitsubishi FX5U Communication Architecture
The FX5U CPU is designed with communication as a first-class feature. Out of the box, every FX5U module includes:
- 1 × Ethernet port (10/100 Mbps) for TCP/IP and UDP communication
- 1 × RS-485 port for serial networking up to 50 nodes
- 1 × RS-485 or RS-232 port (depending on the model variant) for legacy devices
- Optional communication/expansion modules on the left side for additional protocols
This makes the FX5U exceptionally flexible for both greenfield installations and retrofit projects where it must coexist with older serial equipment.
Built-In Communication Ports and Their Specifications
| Port | Type | Max Speed | Typical Use |
|---|---|---|---|
| CH1 / Ethernet | RJ45 (TCP/UDP) | 100 Mbps | HMI, SCADA, GOT, peer-to-peer, SLMP |
| CH2 / RS-485 | 2-wire or 4-wire | 115.2 kbps | Inverter control, multi-drop PLC links, sensors |
| CH3 / RS-485 or RS-232 | Terminal or Mini-DIN | 115.2 kbps | Modbus RTU, bar-code readers, legacy devices |
| Extension modules | FX5-ENET, FX5-CCL, FX5-232/485 | Up to 1 Gbps | CC-Link IE, additional Ethernet ports, Profinet |
Supported Communication Protocols
Mitsubishi designed the FX5U to “speak” almost every industrial language commonly used on the plant floor. The main protocols include:
- MC Protocol (MELSEC Communication Protocol) – the native Mitsubishi protocol used by GX Works3, GOT HMIs, and SCADA tags.
- SLMP (Seamless Message Protocol) – an open Ethernet protocol that allows third-party devices to read/write FX5U memory using a simple 3E or 4E frame format.
- Modbus TCP / Modbus RTU – supported natively over Ethernet and RS-485, allowing simple integration with inverters, energy meters, and third-party PLCs.
- CC-Link and CC-Link IE Field Basic – for high-speed deterministic fieldbus networks.
- N:N Network and Parallel Link – built-in PLC-to-PLC data sharing over RS-485.
- Predefined Protocol Support – GX Works3 includes a library of ready-made function blocks for Omron, Siemens, Yaskawa, Delta and many other vendors.
Configuring FX5U Ethernet Communication
Ethernet setup on the FX5U is performed in GX Works3 under Navigation → Parameter → FX5U CPU → Ethernet Port. The key parameters you must configure are:
- IP Address, Subnet Mask, and Default Gateway
- Open Settings – defines which connections (MELSOFT, MC, SLMP, Modbus) are allowed and on which port numbers
- Connection limits – up to 8 concurrent connections on the built-in Ethernet
- Security settings – IP filter and port blocking to harden the network
Once configured, the FX5U can be accessed by an HMI, a SCADA node, or even a custom Python application using socket communication and the SLMP 3E frame.
Example: Reading a D-Register via SLMP
A typical SLMP read request to fetch 10 words starting from D100 in the FX5U uses the following structure:
| Field | Value |
|---|---|
| Subcommand | 0x0004 (Word Access Random Read) |
| Device Code | 0x0001 (D-Register) |
| Device Number | 100 (decimal) |
| Number of Points | 10 (decimal) |
RS-485 Communication and Modbus RTU
RS-485 is still the workhorse of industrial communication thanks to its long cable runs, noise immunity, and multi-drop capability. On the FX5U, you can use the built-in CH2 port to create a master or slave network of up to 50 devices at distances up to 1200 m (depending on baud rate).
The most common Modbus RTU master instructions available in GX Works3 include:
- ADPRW – generic Modbus read/write used to access holding, input, and coil registers
- IVDR – dedicated inverter read function block
- IVCK / IVCS – Mitsubishi inverter parameter read/write
Connecting the FX5U to HMIs, Inverters, and Other PLCs
One of the strengths of the FX5U is how easily it integrates with the rest of the Mitsubishi ecosystem and with third-party gear. Typical scenarios include:
- GOT2000 / GOT1000 HMI – connect over Ethernet using the built-in GOT driver, or over RS-485 for cost-sensitive machines.
- Mitsubishi Inverters (A800, E800, D700) – control frequency and monitor current using the dedicated FR-A800 or FR-E800 inverter protocol.
- SCADA Systems (Ignition, WinCC, iFIX) – use Modbus TCP or the MC Protocol driver; both are supported natively in most modern SCADA platforms.
- Other PLCs (Siemens S7, Allen-Bradley, Omron) – bridge data using Modbus TCP gateways or predefined protocol blocks in GX Works3.
- Vision Systems and RFID Readers – connect via Ethernet TCP socket or RS-232 using a custom protocol script.
Common Troubleshooting Scenarios
