Q04UDEHCPU is a Universal model CPU module for Mitsubishi Electric’s MELSEC-Q series programmable logic controller platform, offering 40,000 program steps, a basic instruction execution time of 1.9 ns, and built-in USB and Ethernet ports for programming and network communication. As part of the QnUDEH CPU family, the Q04UDEHCPU incorporates built-in CC-Link IE Field Network Basic functionality, multiple file register areas, and an SD memory card slot for data logging and program backup — capabilities that previously required separate option modules on earlier Q-series CPU generations. Available now at Atlantech Drives with worldwide express delivery and 12-month warranty — complete our quote form for pricing and availability.
What Is the Q04UDEHCPU?
The Q04UDEHCPU belongs to Mitsubishi Electric’s Universal model MELSEC-Q CPU range, which represents the final and most capable generation of the Q-series platform before the transition to the iQ-R series. The «04» in the part number denotes the program memory capacity of 40,000 steps, positioning this CPU between the Q02UDEHCPU (20,000 steps) and the Q06UDEHCPU (60,000 steps). The «UDE» suffix identifies it as a Universal model with built-in USB and Ethernet interfaces, and the «H» suffix confirms the high-speed processing variant with the 1.9 ns basic instruction time. The Q04UDEHCPU is backward compatible with all Q-series base units, power supply modules, I/O modules, and intelligent function modules, making it the standard upgrade path for systems running earlier QnA, Q2A, or Basic model Q-series CPUs. It supports multiple CPU configurations (Multi-CPU) of up to 4 CPU modules on a single main base unit, enabling co-processing with motion CPUs (Q172DCPU, Q173DCPU) or C controller modules within the same chassis.
Key Technical Specifications
- Program Memory: 40,000 steps (Flash ROM)
- Basic Instruction Execution Time: 1.9 ns
- I/O Points: Up to 4,096 (with extension bases)
- Device Memory: Internal relay (M): 8,192 points; Data register (D): 12,288 words
- File Register: 32,768 words (standard) — expandable via SD card
- Built-in Ethernet Port: 100BASE-TX, RJ45, supports MELSOFT/SLMP/CC-Link IE Field Network Basic
- Built-in USB Port: Mini-USB, for GX Works2/GX Works3 programming
- SD Memory Card Slot: Supports SDHC up to 32 GB (logging, program backup)
- Multi-CPU Support: Up to 4 CPUs per main base unit
- Interrupt Response Time: 0.21 ms (fixed scan interrupt)
- RTC: Built-in with battery backup
- Power Consumption: 5 V DC, 0.63 A (from Q-series power supply)
- Operating Temperature: 0 °C to 55 °C
- Weight: Approx. 230 g
Series Comparison & Selection Guide
Within the QnUDEH CPU family, selection is primarily driven by program step count and the volume of device memory required. The Q02UDEHCPU (20,000 steps) suits simple machine controllers and standalone process units; the Q04UDEHCPU (40,000 steps) is the most frequently specified variant, covering the majority of medium-complexity automation programs including multi-axis motion coordination, process recipe management, and SCADA gateway functions. The Q06UDEHCPU (60,000 steps) and Q13UDEHCPU (130,000 steps) are appropriate for large-scale systems such as automotive body shop controllers or multi-line packaging systems where a single CPU manages multiple functional areas. The Q26UDEHCPU (260,000 steps) and Q50UDEHCPU (500,000 steps) address plant-wide SCADA and DCS replacement applications. All QnUDEH models share identical hardware interfaces, base unit compatibility, and instruction sets — upgrading from Q04UDEHCPU to a higher step model requires only a CPU module swap and GX Works2 project parameter update, with no changes to I/O wiring or extension module configuration. For new machine designs, Mitsubishi recommends evaluating the iQ-R series (R04CPU and above) as the strategic platform, as the Q-series is in a maintenance lifecycle phase; however, the Q04UDEHCPU remains fully supported and is the correct choice for expanding or maintaining existing Q-series installations.
Troubleshooting Guide
The most common field issues with the Q04UDEHCPU fall into three categories: startup faults, Ethernet communication failures, and battery-related alarms. For startup faults, connect GX Works2 via USB and navigate to Diagnostics → System Monitor to read the error code displayed in the CPU module’s LED status; error codes in the 1000–1999 range typically indicate parameter errors resolvable by re-downloading the PLC parameters, while 2000–2999 range codes indicate hardware faults requiring module replacement. For Ethernet communication failures, verify that the built-in Ethernet port IP address is configured in the PLC parameters (not conflicting with another device on the subnet) and that the port is set to the correct open system protocol (MELSOFT connection uses port 5006 by default for GX Works2). If SLMP (MC Protocol) polling from a SCADA system fails intermittently, check the number of simultaneous connections configured — the Q04UDEHCPU built-in Ethernet port supports a maximum of 16 simultaneous connections, and exceeding this limit causes new connection requests to be silently rejected. Battery alarms (SP.BATTERY or LED flash pattern code 20) indicate the RTC/SRAM backup battery requires replacement; use the Q6BAT lithium battery and replace with the CPU powered on to avoid SRAM data loss. If the SD card slot is used for data logging and write operations cease without error, check available card capacity — the CPU stops writing when free space drops below a configurable threshold defined in the data logging parameter settings.
Frequently Asked Questions
Q: Can the Q04UDEHCPU run programs written for older QnA-series CPUs without modification?
A: The Q04UDEHCPU supports a QnA compatibility mode that allows ladder programs originally written for QnA-series CPUs to execute without full rewriting. However, Mitsubishi strongly recommends converting QnA projects to native Q-series format using GX Works2’s project conversion tool, as compatibility mode disables several performance optimisations and some Universal model instructions are unavailable in QnA mode. Structured text and function block programming is only available in native Q-series project format.
Q: Is the Q04UDEHCPU compatible with the Q-series redundant power supply base units?
A: Yes. The Q04UDEHCPU is compatible with all Q-series main base units including the QA1S5□B redundant power supply base units and the QA□B standard base units in 3, 5, 8, and 12 slot configurations. For redundant CPU configurations (standby redundant systems), the Q04UDEHCPU can be paired with a second Q04UDEHCPU in a Q6□B redundant base unit using the QBF11 or QBF13N tracking cable.
Q: What SD card format and brand is recommended for use with the Q04UDEHCPU?
A: Mitsubishi Electric publishes a compatibility list of validated SD and SDHC cards on the FA Global support portal. Cards not on this list may cause intermittent write errors or initialisation failures. In general, industrial-grade SDHC cards (SLC or MLC NAND with extended temperature rating) from manufacturers such as Panasonic, ATP, or Transcend Industrial are preferred over consumer-grade cards, which have shorter write endurance cycles unsuitable for continuous data logging applications.
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