YOKOGAWA F3RS22-ON Serial Communication Module – FA-M3 Series

YOKOGAWA F3RS22-ON Serial Communication Module – Deterministic Data Exchange at the FA-M3 Backplane Level

The YOKOGAWA F3RS22-ON is a dual-channel serial communication module engineered for the FA-M3 (FACTORY ACE) programmable controller platform. Its primary function within a control loop is to serve as a protocol-transparent serial gateway between the FA-M3 CPU backplane and field devices or supervisory systems that communicate over RS-422 or RS-485 physical layers. Unlike higher-level fieldbus modules that impose protocol overhead, the F3RS22-ON operates at the character-frame level, giving the application program direct control over transmission timing, framing, and error-handling logic. This architecture is particularly relevant in legacy SCADA integrations, serial HMI links, and point-to-point instrument communication where deterministic byte-level latency is a hard requirement.

Within the FA-M3 rack, the module occupies a single slot and communicates with the CPU via the internal high-speed backplane bus. The CPU reads and writes to the module’s dual-port RAM buffer through standard I/O instructions, decoupling the communication task from the main scan cycle. This means that even at a 10 ms CPU scan rate, the serial channels can sustain continuous full-duplex data streams without introducing scan jitter. The module supports baud rates from 300 bps up to 115,200 bps per channel, independently configurable, which allows simultaneous connection of a slow RTU instrument and a high-speed HMI panel on the same module without resource contention.

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Technical Parameters

Hardware Logical Analysis

Photocoupler Isolation Architecture. The F3RS22-ON places optocoupler barriers at the boundary between the 5 VDC backplane logic domain and the RS-422/RS-485 line driver circuitry. This galvanic isolation eliminates ground-loop currents that are endemic in large industrial installations where field devices and control cabinets share separate earthing points. The isolation withstand voltage is rated to handle transient differentials that commonly appear on long cable runs in electrically noisy environments such as motor drive rooms or high-voltage switchgear panels. Practically, this means the module’s UART logic remains unaffected by common-mode noise events that would corrupt data on non-isolated interfaces.

Dual-Port RAM Buffer and Backplane Decoupling. Each channel maintains an independent transmit and receive FIFO buffer in dual-port RAM accessible by both the onboard UART controller and the FA-M3 CPU bus interface. The CPU writes transmit data and reads receive data through mapped I/O registers without waiting for serial line activity to complete. This asynchronous architecture prevents serial communication latency from propagating into the CPU scan cycle — a critical property in applications where the PLC must simultaneously manage fast analog control loops and slower serial instrument polling.

RS-485 Bus Arbitration and Termination. In RS-485 half-duplex mode, the module handles transmit-enable (TE) signal assertion automatically based on the configured transmission timing parameters, eliminating the need for software-managed TE toggling that is a common source of bus contention errors in manually implemented RS-485 drivers. The module’s line driver supports a bus load of up to 32 unit loads, sufficient for multi-drop networks of up to 31 slave devices per channel. Internal termination resistor configuration is handled via DIP switch on the module face, allowing field engineers to set line termination without modifying wiring.

EMC Design Compliance. The module’s PCB layout follows YOKOGAWA’s standard EMC design rules for FA-M3 modules, including ground plane segmentation between digital and analog sections, ferrite bead filtering on power supply rails, and shielded connector housings. The module carries CE marking for the EMC Directive, confirming compliance with EN 61000-6-2 (industrial immunity) and EN 61000-6-4 (industrial emissions) standards.

System Integration Benefits

• Protocol-transparent operation: The F3RS22-ON does not impose a fixed protocol stack. The FA-M3 CPU application program constructs and parses frames directly, enabling support for any serial protocol — Modbus RTU, PROFIBUS DP (via gateway), proprietary instrument protocols, or custom framing — without firmware changes to the module itself.
• Independent dual-channel configuration: CH1 and CH2 operate with fully independent baud rate, data format, and mode settings. A single module can simultaneously serve an RS-422 link to a high-speed barcode reader and an RS-485 multi-drop network of temperature transmitters, reducing slot consumption and wiring complexity.
• Deterministic scan-cycle integration: Because the module buffers serial data in dual-port RAM, the CPU accesses communication data within a fixed, predictable number of instruction cycles. This determinism is essential for closed-loop control applications where communication latency must be bounded.
• Diagnostic transparency: The module exposes channel status flags — framing error, parity error, overrun error, and buffer overflow — as readable I/O registers. The CPU application can log these flags to a historian or trigger alarms without requiring external diagnostic hardware, improving fault traceability in 24/7 production environments.
• Long-distance field device connectivity: RS-485 at 9,600 bps supports cable runs up to 1,200 m, enabling direct serial links to remote field instruments in large plant layouts without repeaters or protocol converters.
• Reduced integration risk with FA-M3 ecosystem: As a native YOKOGAWA module, the F3RS22-ON is fully validated against FA-M3 CPU firmware revisions. There are no third-party driver compatibility issues, and YOKOGAWA’s technical documentation provides complete register maps and ladder logic programming examples.
• Hot-swap and rack flexibility: The FA-M3 platform supports module replacement procedures that minimize downtime. The F3RS22-ON’s configuration parameters are stored in the CPU project, so a replacement module is operational after a CPU download without manual re-parameterization at the module level.
• Scalable multi-module deployment: Multiple F3RS22-ON modules can be installed in the same FA-M3 rack or expansion racks, each addressed independently by the CPU. This allows serial communication capacity to scale linearly with project requirements without architectural redesign.

Quality Assurance & Global Logistics

Every F3RS22-ON unit supplied through siemensplc.com is sourced as genuine YOKOGAWA OEM stock. Each unit undergoes a structured incoming inspection: part marking verification against YOKOGAWA’s published label specifications, physical housing integrity check, and connector pin condition assessment. Units that do not pass inspection are quarantined and not offered for sale. A 12-month warranty against manufacturing defects is provided on all new OEM units.

Logistics operations are based in Xiamen, China — a major export hub with direct access to international express carriers including DHL Express, FedEx International Priority, and UPS Worldwide Expedited. Standard in-stock orders are processed and dispatched within 1–2 business days. For time-critical project requirements, same-day dispatch is available on confirmed orders received before 14:00 CST. All shipments include a commercial invoice, packing list, and can be accompanied by a certificate of origin upon request. Export documentation is prepared in compliance with applicable customs regulations for the destination country. Bulk project orders are supported with consolidated freight options and volume pricing — contact the sales team for a formal quotation.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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