The Mitsubishi FX3U-128MT/ESS is a MELSEC-F series PLC base unit with 64 DC 24 V inputs and 64 transistor source outputs, handling up to 256 local I/O points (384 with remote expansion). It runs on 100-240 VAC, consuming 65 W, and offers a 64K step program memory with a cycle time of 65 ns for LD instructions and 642 ns for MOV. Built-in RS-422 is standard; USB is an option. The unit is expandable via the MELSEC-F extension bus, accepts buffer battery-backed RAM, and is rated IP10 for basic environmental protection. Its operating range is 0–55 °C.
The closest functional peer within the current Mitsubishi PLC line is the FX5U-64MT/DS, which is part of the newer iQ-F series. The FX3U-128MT/ESS offers 64 inputs and 64 outputs, while the FX5U-64MT/DS provides 32 inputs and 32 outputs.