The Q20UDEHCPU is Mitsubishi Electric’s high-performance Universal model CPU for the MELSEC-Q series programmable controller system, offering 20,000 steps of program memory and built-in Ethernet and USB interfaces for seamless integration into modern industrial networks. Designed for demanding discrete and process automation applications, the Q20UDEHCPU operates at an execution speed of 1.0 ns per LD instruction — one of the fastest in the MELSEC-Q lineup — making it suitable for high-speed, precision-critical manufacturing environments. Available now at Atlantech Drives with worldwide express delivery and 12-month warranty — complete our quote form for pricing and availability.
What Is the Q20UDEHCPU?
The Q20UDEHCPU is a Universal model CPU module belonging to Mitsubishi Electric’s MELSEC-Q series, the company’s flagship modular PLC platform for mid-to-large-scale industrial automation. The «UDEH» designation indicates that this CPU belongs to the Universal model Enhanced High-speed family, combining extended memory capacity, dual built-in communication ports, and high-speed processing in a single compact module. The Q20UDEHCPU supports a program memory capacity of 20,000 steps (or up to 80,000 steps when using an extended SRAM memory card), making it well suited for complex machine sequencing, motion coordination, and process control applications. The module mounts directly into any MELSEC-Q series base unit (Q3B, Q5B, Q6B, Q12B, Q25B) and is fully compatible with the broader MELSEC-Q I/O, analogue, communication, and positioning module ecosystem. The Q20UDEHCPU supports both ladder logic (LD) and structured text programming via GX Works2 and GX Works3 engineering software.
Key Technical Specifications
- Model: Q20UDEHCPU
- Series: MELSEC-Q Universal Enhanced High-speed
- Program Memory: 20,000 steps (expandable to 80,000 steps with memory card)
- Execution Speed: 1.0 ns per LD instruction
- I/O Points: Up to 4,096 (local) / 8,192 (remote)
- Built-in Interfaces: Ethernet (100BASE-TX), USB (mini-B)
- Number of Mountable Modules: Up to 64 modules per base
- Power Supply Voltage: 5 VDC (supplied via base unit)
- Operating Temperature: 0°C to 55°C
- Weight: Approx. 0.19 kg
- Compatible Base Units: Q3B, Q5B, Q6B, Q12B, Q25B, Q32B, Q33B, Q35B, Q38B, Q312B
- Programming Software: GX Works2, GX Works3
Compatibility & System Integration
The Q20UDEHCPU is designed for seamless integration within the MELSEC-Q modular architecture. It is compatible with the full range of MELSEC-Q I/O modules (QX/QY series), analogue modules (Q64AD, Q68ADV, Q62DA), high-speed counter modules (QD62, QD62E), positioning modules (QD75MH, QD77MS), and communication modules (QJ71E71-100 Ethernet, QJ71MT91 MODBUS, QJ61BT11N CC-Link). The built-in Ethernet port supports SLMP (Seamless Message Protocol), allowing direct communication with GOT HMI terminals, SCADA systems, and MES platforms without an additional communication module. The Q20UDEHCPU also supports redundant CPU configuration when paired with the Q3MDBR base unit and a matching Universal CPU, enabling hot-standby redundancy for critical continuous-process applications. For motion control integration, the CPU can be combined with the Q170MCPU motion controller in a multi-CPU configuration, sharing I/O data at high speed via the MELSEC-Q inter-CPU communication mechanism.
Installation Advice
Before installing the Q20UDEHCPU, ensure the base unit is de-energised and the power supply module is disconnected. The CPU module must always be inserted into slot 0 (the leftmost slot) of the base unit — inserting it in any other slot will result in a hardware error and the system will not initialise. When mounting the module, align the connector and press firmly until the module lock mechanism clicks into place; do not apply lateral force during insertion. For systems using the built-in Ethernet port, use a Category 5e or higher shielded cable and connect to a managed industrial switch — unmanaged consumer-grade switches can cause intermittent communication timeouts in high-traffic environments. After power-up, verify the RUN LED is solid green and the ERR LED is off before loading the user program. If the ERR LED flashes on first power-up, check that the correct power supply module (Q61P, Q62P, or Q63P) is installed and that the total current draw of all installed modules does not exceed the base unit’s rated capacity.
Frequently Asked Questions
Q: Can the Q20UDEHCPU be used as a replacement for the Q20HCPU in an existing MELSEC-Q installation?
A: Yes, the Q20UDEHCPU is the direct successor to the Q20HCPU and is backward compatible with existing MELSEC-Q base units and I/O modules. However, the program must be re-verified in GX Works2 or GX Works3 after substitution, as some special relay and register assignments differ between the H and UDEH models. Parameter settings for built-in Ethernet must also be reconfigured, as the Q20HCPU required a separate QJ71E71 Ethernet module whereas the Q20UDEHCPU has Ethernet built in.
Q: What is the maximum number of I/O points supported by the Q20UDEHCPU in a multi-base configuration?
A: In a multi-base configuration using extension base units (Q6B, Q12B, Q25B), the Q20UDEHCPU supports up to 4,096 local I/O points. When remote I/O stations are added via CC-Link (QJ61BT11N) or MELSECNET/H, the total addressable I/O can be extended to 8,192 points. Each extension base requires a power supply module and a base connector cable (QC series).
Q: Does the Q20UDEHCPU support online program change during machine operation?
A: Yes. The Q20UDEHCPU supports online program change (OPC) from GX Works2 and GX Works3, allowing ladder rungs and SFC steps to be added, modified, or deleted while the CPU is in RUN mode. The change is applied at the end of the current scan cycle without interrupting machine operation. However, online change is subject to the constraint that the total program memory after the change must not exceed 20,000 steps (or the extended capacity if a memory card is installed).
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