FX3U-4HSX-ADP is a 4-channel high-speed input adapter for Mitsubishi Electric’s MELSEC FX3U and FX3UC series programmable logic controllers, extending the built-in high-speed counter capability of the FX3U CPU with four additional differential line driver input channels capable of counting at up to 200 kHz per channel. Designed as a left-side adapter unit, the FX3U-4HSX-ADP connects to the FX3U CPU without consuming any extension I/O slots, making it the preferred solution when high-speed encoder or pulse input capacity must be added to a fully populated FX3U system. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the FX3U-4HSX-ADP?
The FX3U-4HSX-ADP is a left-side special adapter that mounts directly onto the left side of the FX3U or FX3UC CPU module, ahead of any left-side communication modules such as the FX3U-ENET-L. Up to two FX3U-4HSX-ADP adapters can be stacked on a single FX3U CPU, providing a maximum of 8 additional high-speed input channels beyond the CPU’s built-in counter inputs. Each of the four channels accepts differential line driver signals (RS-422 compatible, A/B/Z phase) from incremental rotary encoders, linear scales, or pulse generators, and feeds these signals directly into dedicated high-speed counter hardware within the adapter — bypassing the FX3U CPU scan cycle entirely and ensuring no missed counts regardless of the ladder program execution time. The counter values are accessible from the FX3U CPU via special data registers (SD and buffer memory areas) using FROM/TO instructions or direct device mapping depending on the firmware version.
Key Technical Specifications
- Number of Input Channels: 4 (A-phase, B-phase, Z-phase per channel)
- Input Signal Type: Differential line driver (RS-422), 5 V DC
- Maximum Count Frequency: 200 kHz per channel
- Counter Resolution: 32-bit signed integer (±2,147,483,647)
- Count Modes: 1-phase 1-count, 1-phase 2-count, 2-phase 1-count, 2-phase 4-count (quadrature)
- Z-phase (index pulse) input: Supported per channel for position reset
- Maximum Adapters per CPU: 2 (total 8 additional high-speed channels)
- Power Supply: 5 V DC, 120 mA (from FX3U left-side bus)
- Compatible Base Units: FX3U, FX3UC (with FX3UC-1PS-5V)
- Operating Temperature: 0 °C to 55 °C
- Dimensions (W × H × D): 40 × 90 × 87 mm
- Weight: Approx. 160 g
Architecture & Design Overview
The FX3U-4HSX-ADP implements dedicated counter hardware independently of the FX3U CPU’s main processing loop. This architectural separation is the critical differentiator from the FX3U’s built-in high-speed counters (C235–C255), which also operate independently of the scan cycle but are limited to single-ended 24 V DC input signals at a maximum of 100 kHz. The FX3U-4HSX-ADP’s differential RS-422 input circuitry provides common-mode noise rejection of typically 7 V, making it significantly more robust in electrically noisy environments — such as those with variable frequency drives, servo amplifiers, or induction heating equipment nearby — compared to single-ended 24 V DC encoder inputs. In 2-phase 4-count (quadrature ×4) mode, each physical encoder pulse edge generates a count increment, meaning a 2,500 PPR encoder effectively yields 10,000 counts per revolution of position resolution. The Z-phase index input on each channel can be configured to reset the channel counter to zero or to a preset value on each index pulse, enabling absolute-within-one-revolution positioning from an incremental encoder without external reset circuitry. Counter comparison outputs (triggered when the counter reaches a preset value) are available as internal flag devices accessible within the FX3U ladder program, allowing high-speed position-triggered actions without waiting for the next scan cycle completion.
Expert Tips
When connecting differential line driver encoders to the FX3U-4HSX-ADP, verify that the encoder’s supply voltage matches the adapter’s 5 V DC input specification — many industrial encoders offer selectable 5 V or 24 V output levels, and connecting a 24 V line driver output to the FX3U-4HSX-ADP input will damage the differential receiver IC. Use individually shielded twisted-pair cable (such as Belden 9842 or equivalent) for encoder signal wiring, with the shield grounded at the adapter end only to prevent ground loop currents from corrupting the differential signal. For cable runs exceeding 30 m, verify that the line driver output current of the encoder is sufficient to maintain signal integrity at 200 kHz — use the encoder manufacturer’s cable length vs. frequency derating curve. When stacking two FX3U-4HSX-ADP adapters on a single FX3U CPU, the second adapter (farther from the CPU) is addressed as the second adapter in the FROM/TO buffer memory mapping — confirm the address offset in the FX3U-4HSX-ADP User’s Manual (JY997D31201) before writing the counter read routine, as address mapping errors are the most common commissioning mistake with stacked adapters. If the FX3U-ENET-L is also installed on the left side, the adapter stack order is: CPU → FX3U-4HSX-ADP → FX3U-ENET-L, not the reverse.
Frequently Asked Questions
Q: Can the FX3U-4HSX-ADP be used with single-ended (open collector or push-pull) encoder outputs?
A: No. The FX3U-4HSX-ADP accepts only differential line driver (RS-422) signals. For single-ended 24 V DC encoder outputs, the FX3U’s built-in high-speed counter inputs (X000–X005) should be used instead, which are rated for 24 V DC single-ended signals at up to 100 kHz. Alternatively, a line driver signal converter can be inserted between a single-ended encoder and the FX3U-4HSX-ADP, though this adds cost and wiring complexity.
Q: Does the FX3U-4HSX-ADP work with the FX3G or FX3S CPU series?
A: No. The FX3U-4HSX-ADP is mechanically and electrically specific to the FX3U and FX3UC left-side expansion bus. The FX3G and FX3S series use a different left-side adapter architecture and are not compatible with this unit.
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