The FX2N-128MR-ES/UL is Mitsubishi Electric’s 128-point relay output base unit for the MELSEC FX2N compact PLC series — the highest I/O count ever produced in any FX2N base unit configuration — providing 64 digital inputs and 64 relay contact outputs in a self-contained AC-powered controller with UL listing for North American installations. As the absolute maximum-capacity FX2N base unit, the FX2N-128MR-ES/UL was specified for the most complex standalone machine control applications of the FX2N era, commanding the highest scarcity premium of any FX2N relay output model and representing the most critical maintenance replacement scenario for facilities operating large-format machines built around this unit. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX2N-128MR-ES/UL?
The FX2N-128MR-ES/UL is a MELSEC FX2N series compact PLC base unit providing 64 input points (X0–X77, octal numbering) and 64 relay contact output points (Y0–Y77, octal), in the largest housing produced for the FX2N platform with a built-in 100–240 VAC power supply. The 64 relay outputs are organised in eight independent common groups of 8 points each — the maximum number of independent common groups in any FX2N base unit — providing exceptional voltage-zone assignment flexibility for complex multi-voltage machine panels where different sections of field devices operate at 24 VDC, 48 VDC, 110 VAC, and 230 VAC from the same PLC. The FX2N CPU architecture is identical to all other FX2N base units: 0.08 µs per basic instruction, 8,000-step standard program memory expandable to 16,000 steps with the FX2N-ROM-E1 memory cassette, 4 built-in high-speed counter inputs at up to 60 kHz single-phase, and pulse output on Y0 at 20 kHz. With 128 total I/O points on the base unit alone, the FX2N-128MR-ES/UL approaches the FX2N platform’s 256-point maximum expansion capacity — leaving only 128 points of address space for extension modules, which is typically more than sufficient for the supplementary I/O requirements of systems using this large base unit.
Key Technical Specifications
- Model: FX2N-128MR-ES/UL
- Total I/O Points: 128 (64 inputs + 64 outputs)
- Input Type: 24 VDC sink (X0–X77)
- Output Type: Relay contact (Y0–Y77), 2 A per point, 240 VAC / 30 VDC
- Output Common Groups: 8 groups of 8 points (independent commons)
- Power Supply: 100–240 VAC, 50/60 Hz
- Certification: UL listed
- Program Memory: 8,000 steps (16,000 with FX2N-ROM-E1 cassette)
- Execution Speed: 0.08 µs per LD instruction
- Built-in High-Speed Counters: 4 inputs (60 kHz single-phase)
- Built-in Pulse Output: Y0 up to 20 kHz
- Communication: RS-422 (built-in)
- Battery: FX2N-1BL or FX2N-32BL lithium battery
- Expansion: Up to 256 total I/O via FX2N extension modules
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 350 mm × 90 mm × 87 mm
- Weight: Approx. 1.90 kg
Architecture & Design Overview
The FX2N-128MR-ES/UL implements the standard FX2N CPU architecture in the largest available base unit housing, with 8 independent relay output common groups each consisting of 8 relay contact output points sharing one common terminal. The eight independent commons enable simultaneous control of loads at up to eight different voltage levels from a single base unit — a requirement unique to large multi-section process machines where field devices across different subsystems operate at different supply voltages determined by legacy electrical standards, regional requirements, or functional differentiation (24 VDC control valves, 110 VAC instrument heating, 230 VAC motor contactors, 48 VDC safety devices). The relay output driver board uses individual electromechanical relays per output point, with optical isolation between the FX2N CPU logic circuit and the relay driver stage providing galvanic isolation between the PLC logic supply and the field load circuits. The 8,000-step standard program memory — which may appear modest relative to the 128-point I/O capacity — reflects the FX2N design philosophy of dense I/O in a compact package, with the understanding that large relay output applications (conveyor staging, valve sequencing, motor starter sequencing) are typically implemented in straightforward ladder logic that is compact in program step count despite controlling many I/O points. The FX2N-ROM-E1 memory cassette doubles available program space to 16,000 steps and provides non-volatile program storage independent of the battery — strongly recommended for the FX2N-128MR-ES/UL given the complexity and value of machines typically controlled by this large base unit.
Expert Tips
For FX2N-128MR-ES/UL installations where the 8,000-step standard program memory is approaching its limit, install the FX2N-ROM-E1 memory cassette before reaching 100% capacity — attempting to add new ladder rungs to a full FX2N program memory triggers a memory full error in GX Works2 that prevents program download, requiring an immediate solution in a maintenance scenario where machine downtime is costly. The FX2N-ROM-E1 cassette should be treated as standard equipment on the FX2N-128MR-ES/UL given the complexity of programs typically associated with 128-point I/O systems. For the eight relay output common groups, document the voltage assignment for each common group on the inside of the panel door and in the electrical drawings — maintenance technicians unfamiliar with the specific installation may not recognise that adjacent common group terminals carry different voltage levels, creating a shock or short-circuit hazard during wiring work. Use different wire colours or marking labels for each common group voltage to reinforce the documentation at the terminal block level. For long-term spare parts management, the FX2N-128MR-ES/UL is the scarcest FX2N relay output model due to its large size and the disproportionately high cost of platform migration for complex 128-point relay machines — facilities operating more than 3 units of this model should maintain a minimum of one spare unit in inventory. When storing spare FX2N-128MR-ES/UL units, remove the battery from the spare unit to prevent battery depletion during storage, and store the battery separately in original packaging — an FX2N base unit stored for 2+ years with its battery installed will typically have a depleted battery requiring replacement before the spare can be deployed.
Frequently Asked Questions
Q: What is the closest current-production Mitsubishi PLC equivalent to the FX2N-128MR-ES/UL?
A: The FX3U-128MT/ES-A and FX3U-128MT/ESS provide 128 total I/O points (64 inputs + 64 outputs) in transistor output configuration — the closest current FX3U base unit in I/O count. However, there is no current-production Mitsubishi compact PLC with 64 relay output points in a single base unit. For 64 relay output coverage on a current platform, the FX3U-80MR/ES-A (40 relay outputs) with FX3U-16EYR relay output extension modules (providing 16 additional relay outputs per module) can reach 64 relay outputs — base unit (40) + 1.5 extension modules (24 additional) = 64 total relay outputs. Alternatively, the MELSEC iQ-F FX5U-64MR/ES provides 32 relay outputs from the base unit with the option to expand via extension modules to the required relay output count.
Q: Can the FX2N-128MR-ES/UL’s battery be replaced while the unit is powered and running, to avoid program loss?
A: Yes, but with a strict time constraint. Replacing the battery while the FX2N-128MR-ES/UL is powered on allows the internal SRAM capacitor to maintain data during the brief battery removal period — the capacitor provides approximately 20 seconds of backup during battery-less powered operation. Remove the old battery, insert the new FX2N-1BL battery, and verify polarity within 20 seconds to prevent SRAM data loss. It is strongly recommended to take a GX Works2 program backup to a PC before any battery replacement on the FX2N-128MR-ES/UL, as insurance against data loss if the replacement takes longer than 20 seconds.
Q: Does the FX2N-128MR-ES/UL require any special power supply beyond the standard 100–240 VAC panel supply?
A: No. The FX2N-128MR-ES/UL’s built-in power supply accepts 100–240 VAC single-phase at 50/60 Hz and generates all required internal DC voltages (5 VDC for CPU logic, 24 VDC for input sensor supply) internally. No external 24 VDC supply is required for the PLC itself. The relay output load circuits require an external supply appropriate to the load voltage — each common group’s external load supply is connected to the group’s COM terminal, with the voltage rating and current capacity determined by the loads connected to that group.
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