Omron CJ1W-SCU21-V1 Serial Communication Unit

The Omron CJ1W-SCU21-V1 is a serial communication unit for the CJ1 and CJ2 series programmable logic controllers. This unit provides two independent serial ports: one RS-232C port and one RS-422A/485 port, allowing the CJ1/CJ2 CPU to communicate with a wide range of external serial devices including HMIs, barcode readers, printers, drives, and third-party PLCs. The SCU21 supports multiple protocols including Host Link (standard Omron PLC protocol), Modbus RTU Master and Slave, no-protocol (for free format communication), and NT Link (for connection to Omron NS/NT series HMIs). Additionally, the unit supports Protocol Macro functionality, which allows users to create custom communication sequences for devices with proprietary protocols, significantly extending the versatility of the CJ1 platform. The SCU21 is ideal for applications requiring serial data acquisition, device configuration, or communication with legacy serial equipment. It is part of Omron's modular CJ series I/O family and occupies one slot in a CJ series rack.

Technical Specifications

The CJ1W-SCU21-V1 has two serial ports: Port 1 is RS-232C (9-pin D-sub male) and Port 2 is RS-422A/485 (terminal block). Supported baud rates: 1.2, 2.4, 4.8, 9.6, 19.2, 38.4, 57.6, and 115.2 kbps (maximum). Transmission distances: RS-232C: up to 15 meters; RS-422A/485: up to 500 meters. Isolation: 500 V AC between communication lines and internal circuits. Protocol support: Host Link (FINS), Modbus RTU (master/slave), NT Link (1:N connections), no-protocol (free format), and Protocol Macro (user-defined sequences). The Protocol Macro functionality supports up to 999 steps per sequence, 512 send/receive words, and up to 100 protocol macros can be stored. The unit includes dedicated DM and CIO areas for control and status bits. Power consumption: 5 V DC, 0.15 A from backplane. Dimensions: 90 mm (H) × 45 mm (W) × 85 mm (D). Protection rating: IP20. The SCU21-V1 is the version 1 iteration of the SCU21 unit, with earlier firmware; version 2 units offer additional features but the V1 provides basic functionality for most applications.

Key Features

• 2 independent serial ports (1 RS-232C, 1 RS-422A/485) for flexible connectivity

• Host Link protocol support for direct connection to Omron PLCs and HMIs

• Modbus RTU master/slave for communication with third-party sensors and drives

• No-protocol mode for free-format ASCII/binary communication

• NT Link for connection to Omron NS/NT touchscreen HMIs

• Protocol Macro function for custom communication sequences

• Built-in hardware handshake (RS-232C) and automatic flow control (RS-422A/485)

• 500 V AC isolation between communication lines and internal logic

• Easy I/O mapping via dedicated CIO and DM areas

• 1:N connection support for multiple slave devices (RS-422A/485)

Protocol Support

The Host Link protocol, Omron's original serial protocol, is used for communication with Omron PLCs, HMIs (NV, NS, NT series), and host computers. Host Link supports both 1:1 and 1:N (multi-drop) connections. The Modbus RTU Master function allows the CJ1 CPU to read and write data to any Modbus RTU slave devices such as temperature controllers, drives, and sensors. As a Modbus RTU slave, the SCU21 can be polled by a Modbus master device. The No-Protocol mode (also known as "no-protocol" or "free format") allows the user to define the exact format of data sent and received, enabling connection to custom devices, printers, and barcode readers. The NT Link protocol is designed for connection to Omron's NS and NT touchscreen series HMIs, enabling fast, high-speed data exchange using Omron's proprietary protocol. The Protocol Macro function is the most powerful feature, allowing users to define custom communication sequences (including protocol definitions such as ASCII, binary, or manufacturer-specific) without writing custom ladder logic code. Protocol macros can be triggered from the ladder program, sending commands to devices and receiving responses without dedicating CPU time to protocol interpretation.

Configuration and Programming

The CJ1W-SCU21-V1 is configured using Omron CX-Programmer software. The unit must be registered in the I/O table, and each port is configured individually for protocol type, baud rate, data length, parity, stop bits, and flow control (for RS-232C). For Modbus RTU, additional parameters such as slave address and response timeout are set. For the Protocol Macro function, users must create protocol macros offline using the Protocol Macro Support Tool software (part of CX-Programmer). Protocols are defined as a series of send/receive sequences, with each step defining the message frame, expected response, and processing of received data. Up to 100 different protocols can be stored on the unit, each supporting up to 999 steps, with a maximum of 512 send words and 512 receive words per sequence. The ladder program triggers protocol execution using dedicated control bits and receives data in system-defined DM addresses.

Applications

The CJ1W-SCU21-V1 is used in industrial automation applications requiring serial communication. Typical uses include connecting temperature controllers (such as Omron E5 series) to a CJ1/CJ2 PLC via Modbus RTU or host link, reading data from barcode scanners or RFID readers in material handling and packaging lines, controlling variable frequency drives via Modbus RTU for speed reference and status monitoring, printing production reports to serial printers, communicating with weigh scales and other industrial measuring instruments, and connecting to legacy serial equipment in retrofit projects. In building automation, the SCU21 connects the CJ1/CJ2 to BACnet MS/TP devices via protocol macro or to Modbus RTU devices used for lighting control and HVAC. In water treatment, it is used to read flow meters and chemical analyzers, sending data to the PLC for process control and alarm management.

Installation and Wiring

The CJ1W-SCU21-V1 installs into any I/O slot of a CJ1 or CJ2 series rack. The unit is secured with screws on the top and bottom of the module. Wiring for the RS-232C port uses a standard 9-pin D-sub male connector. For RS-422A/485, a terminal block is provided; wiring must be done carefully to ensure proper termination and biasing (especially for long runs). Shielded twisted-pair cable should be used for RS-422A/485 connections. The RS-422A/485 port supports both 2-wire (half-duplex) and 4-wire (full-duplex) configurations. Termination resistors (120 Ω) may be required at both ends of the line for RS-422A/485; the SCU21-V1 includes selectable termination via DIP switches. The unit must be properly grounded to avoid noise issues; a grounding wire should be connected to the CJ series rack's ground terminal. After installation, the unit's I/O table must be updated in CX-Programmer. The unit is automatically assigned a unit number (0-7 for SCU21), which determines the memory addresses for control, status, and received data.

Conclusion

The Omron CJ1W-SCU21-V1 serial communication unit provides flexible, high-performance serial connectivity for CJ1/CJ2 PLC systems. Its two independent ports, support for multiple protocols (Host Link, Modbus RTU, no-protocol, NT Link), and powerful Protocol Macro functionality make it a versatile solution for applications requiring communication with serial devices. Whether interfacing with legacy equipment, connecting to third-party instruments, or enabling custom protocol implementations, the SCU21 enhances the connectivity of the CJ/CJ2 platform.