Complete Mitsubishi PLC Migration Guide: Converting FX3U Projects to FX5U in GX Works3
1. Strategic Drivers for Migrating from FX3U to FX5U (MELSEC iQ-F)
The Mitsubishi MELSEC-F FX3U series has anchored industrial machine control globally for over 15 years. Following Mitsubishi Electric's formal End-of-Life (EOL) discontinuation announcements, spare unit procurement has become increasingly constrained and costly. Migrating to the MELSEC iQ-F (FX5U) architecture delivers transformative engineering advantages: - Processor Execution Velocity: Fundamental LD instruction scan times are reduced by 50%, dropping from 65 nanoseconds (FX3U) to 34 nanoseconds (FX5U). - Embedded Communication Infrastructure: The FX5U integrates an onboard 100 Mbps Ethernet port (supporting CC-Link IE Field Basic, Modbus/TCP) and an RS-485 serial port, removing the need for costly external comm modules. - Integrated Motion Control: Transistor output CPUs provide 4-axis 200 kHz independent high-speed pulse outputs complete with embedded linear and circular interpolation routines.
2. Special Device Mapping Matrix (FX3U M/D to FX5U SM/SD)
| System Control Function | Legacy FX3U Device | Target FX5U Device | Migration & Conversion Note |
|---|---|---|---|
| Always ON Contact | M8000 | SM400 | Automatically translated by GX Works3 conversion utility |
| Always OFF Contact | M8001 | SM401 | Directly substituted with SM401 |
| Initial Power-Up Scan Pulse | M8002 | SM402 | Pulses ON for single first scan cycle for system parameter initialization |
| 1.0-Second Clock Pulse | M8013 | SM412 | 50% duty cycle (0.5s ON / 0.5s OFF) identical behavior |
| 100-Millisecond Clock Pulse | M8012 | SM410 | Ideal for panel fault lamp flasher synchronization |
| Instruction Error Flag | M8067 | SM0 | FX3U error codes reside in D8067; FX5U logs error codes in <strong>SD0</strong> |
| Battery Low Voltage Warning | M8005 | SM51 | FX5U features a battery-less flash memory execution architecture |
3. Step-by-Step Project Conversion in GX Works3
- Import Legacy Project Archive: Launch GX Works3, navigate to `Project > Open Other Format File > Open Other Project`, and browse to the FX3U workspace (*.gxw or *.gpp format).
- Execute Module Type Conversion: Select `Project > Change Module Type`. Change target series to FX5CPU and assign CPU model matching required physical I/O count (e.g. `FX5U-32MT/ES`).
- Run Comprehensive Syntax Rebuild: Hit `F4` or select `Convert > Rebuild All`. The compiler parses all ladder rungs, identifying unsupported legacy instructions.
- Remediate Syntax Errors: Review Output log console. Manual intervention is typically required for legacy `RS` serial instructions (transitioned to Module Parameters) and pulse outputs (`PLSY`/`PLSR`), which benefit from transition to modern positioning table instructions.
- Configure Module Parameters: Access `Parameter > FX5UCPU > Module Parameter` to assign network IP addressing and configure high-speed input hardware counters.
4. Hardware Retrofit & Control Cabinet Re-Wiring
While the external footprint of the FX5U matches the FX3U within millimeters, several physical differences require careful field planning: 1. Detachable Terminal Blocks: The FX5U features two-piece pluggable M3 screw terminal blocks, greatly accelerating field replacement but featuring slightly tighter screw spacing. 2. Auxiliary 24VDC Service Power: Onboard 24VDC sensor power capacity is boosted to 480 mA (on 32-point CPUs), frequently eliminating external auxiliary DC power supplies. 3. Pulse Output Phasing: High-speed pulse outputs are consolidated across outputs `Y0, Y1, Y2, Y3` (each rated for 200 kHz). Electricians must cross-reference servo drive CN1 connector schematics before terminating cables.