Mitsubishi FX3U-128MT/ESS PLC CPU Module

The Mitsubishi FX3U-128MT/ESS is a high-performance programmable logic controller from the FX3U series. It features a total of 128 built-in I/O points: 64 digital inputs (24V DC, sink/source) and 64 transistor sink outputs (24V DC, 0.5A per point). The “MT” designation indicates transistor (sink) outputs, while “ESS” signifies compliance with European safety standards. This CPU offers fast execution (0.065 µs per basic instruction), large memory (64K steps), and extensive expansion capabilities. It is suitable for complex automation tasks in packaging, material handling, and machine control. The built-in RS-422 port allows programming and connection to HMIs, and an optional Ethernet or CC-Link module can be added for networking.

Technical Specifications

Power supply: 24V DC (20.4-28.8V). I/O points: 64 inputs, 64 outputs (total 128). Input type: DC sink/source (24V, 4.0mA typical). Output type: transistor sink (NPN), 0.5A per point, 8A per common. Program memory: 64K steps (RAM, battery-backed). Basic instruction speed: 0.065 µs (LD). Application instruction speed: 0.5 µs (MOV). Memory types: RAM, EEPROM (optional cassette). Built-in communication: RS-422 (programming port), and one RS-232/485 optional adapter. High-speed counters: 8 channels, max 100 kHz (single-phase). Pulse outputs: 2 channels, max 100 kHz (transistor outputs). Number of expansion modules: up to 8 (max I/O 384). Dimensions: 130mm (W) × 86mm (H) × 86mm (D). Weight: 0.6 kg. Operating temperature: 0°C to 55°C. Storage: -20°C to 70°C.

Key Features

• 128 built-in I/O (64 in, 64 out transistor sink)

• High-speed processing: 0.065 µs per basic instruction

• 64K steps program memory

• Built-in RS-422 programming port

• Supports up to 8 expansion modules (maximum 384 I/O)

• High-speed counters (100 kHz) and pulse outputs (100 kHz)

• Real-time clock (battery-backed)

• Supports positioning, analog, and temperature control modules

• Compatible with GX Works2 and GX Developer software

Memory and Expansion

The CPU has 64K steps of RAM, backed by a lithium battery (life approx. 5 years). An optional EEPROM cassette can store the program permanently. The CPU can control up to 384 I/O points by adding up to 8 expansion units (e.g., FX2N series I/O modules). Special function modules (analog, positioning, temperature) can also be added. The built-in high-speed counters (100 kHz, 8 channels) can be used for encoder feedback. Two transistor outputs can be configured as 100 kHz pulse trains for stepper motor control.

Programming and Software

Programming is done with Mitsubishi GX Works2 or GX Developer (IEC 61131-3 languages: Ladder, SFC, ST, FBD). The CPU supports function blocks, structured text, and online editing. A user-friendly instruction set includes advanced math, PID, and data conversion instructions. The built-in RS-422 port allows direct connection to a PC via USB-to-RS422 converter (SC-09 cable). An optional RS-232C or RS-485 adapter board can be installed for communication with Modbus devices.

Applications

The FX3U-128MT/ESS is used in mid-range automation systems such as packaging machines (capping, labeling), small assembly lines, material handling equipment, printing presses, and special-purpose machinery. The high-speed inputs are ideal for counting products on a conveyor, and the pulse outputs can control servo or stepper motors for positioning tasks.

Installation and Wiring

Mount the CPU on a DIN rail or directly to a panel. Connect 24V DC power to terminals L+ and M. For inputs, connect sensors between the input terminal and common (COM). Inputs are sink/source configurable via common connection. Outputs are NPN (sink); connect the load between the output terminal and the load supply positive (+24V). Each output group (8 points) has a common terminal (COM). Use external fuses for each common. The programming port is a 8-pin mini-DIN. Expansion modules connect via the expansion cable.

Maintenance and Diagnostics

The CPU has status LEDs for POWER, RUN, BATTERY, ERROR. A blinking ERROR LED indicates a program error or watchdog timeout. Use GX Works2 to read the error code. The battery should be replaced every 5 years (type CR2032). The CPU has a built-in real-time clock that can be set via programming software.

Environmental and Compliance

The FX3U-128MT/ESS is CE, UL, and RoHS compliant. Operating temperature: 0-55°C. Storage: -20-70°C. Humidity: 10-90% non-condensing. Protection rating: IP20.

Conclusion

The Mitsubishi FX3U-128MT/ESS offers a powerful, expandable platform with 128 built-in I/O, high-speed processing, and versatile programming options. It is well-suited for medium-scale automation requiring both discrete I/O and motion control capabilities.