Omron TCP/RTU Communication

This documentation explains how to use Omron FINS Host Link for communication between PLCs, HMIs, and SCADA systems. Omron FINS Host Link describes both the ASCII-based serial Host Link protocol and the binary FINS protocol over TCP/IP. Here you will find the main differences, the Omron memory model, and practical configuration points for both protocols.

Important Protocols

1. Host Link – serial communication (similar to Modbus RTU)
2. FINS – network communication over Ethernet/TCP/IP (similar to Modbus TCP in role)

What is Host Link (RTU)

Host Link is an ASCII-based serial protocol that allows a host (PC, HMI, or SCADA) to send commands in ASCII frames to an Omron PLC. It operates on a master/slave model: the host requests, and the PLC responds. Host Link typically runs over RS-232 or RS-422/485 and supports both one-to-one and multidrop connections. The frames are human-readable (hex values in ASCII), which facilitates debugging and manual testing.

Technical Features of Host Link

Key points to remember for Host Link:

1. Transport: Serial via RS-232 or RS-422/485.
2. Frame format: ASCII frames with a fixed structure, for example, @<node><command>…*<FCS><CR>. The FCS (Frame Check Sequence) ensures error detection.
3. Communication parameters: Baud rate, data bits, parity, and stop bits must match (often 7E2 or 8N1).
4. Polling: The host sends commands; the PLC responds within a fixed time window.
5. Typical functions: Reading/writing DM or CIO areas and reading PLC status.

What is FINS (TCP)

FINS (Factory Interface Network Service) is Omron’s binary network protocol for communication over Ethernet or serial networks. With FINS over TCP/IP, a FINS Client (e.g., SCADA or PC application) and a FINS Server (PLC) exchange data via TCP ports (standard is port 9600). FINS supports more functions than Host Link, such as memory read/write, starting/stopping PLCs, and program upload/download.

Network Configuration and Addressing

For FINS, the following points are important:

1. IP subnet: PLC and client often need to be on the same IP subnet.
2. Port: Standard TCP port 9600 for FINS.
3. Node/Network/Unit addresses: Each device has a Network, Node, and Unit address that must be correctly configured in both the PLC and the client.
4. Routing: The FINS Routing Table enables routing between multiple networks.

Key Features Compared

Supported Devices and Applications

Omron Memory Model

Omron uses fixed memory areas with specific functions, similar to Modbus register types. Commonly used areas include CIO, W (Work), H (Holding), DM, T/C (Timer/Counter), and A (Auxiliary). Below is a brief overview.

Practical Examples and Addressing

Examples of commonly occurring addresses:

1. CIO 0.00 → physical input bit 0
2. CIO 100.00 → physical output bit 100
3. DM0000 → first 16-bit memory word for user data
4. DM0100–DM0199 → often used for analog values or SCADA communication

As with Modbus, always consult the documentation or the PLC program to determine which addresses have which functions.

Setting up a Host Link (RTU) Connection

Steps to configure Host Link:

1. Physical connection: RS-232 or RS-485 cabling with correct pin-out; direct connection or via a communication unit, depending on the PLC type.
2. Communication parameters: Set baud rate, data bits, parity, and stop bits correctly, and ensure a unique node address for multidrop connections.
3. Frame settings: Use the correct ASCII frame structure and FCS for error detection.
4. Polling and timing: Ensure that the host polls and processes within the expected time window.

Setting up a FINS (TCP) Connection

Steps to configure FINS over TCP:

1. Network configuration: Place the PLC and SCADA/PC in the same IP subnet or configure routing correctly.
2. Port: Verify that port 9600 (TCP) is available and not blocked.
3. Node and network addresses: Configure Network, Node, and Unit addresses in both the PLC and the client.
4. Client-server: The client establishes a TCP connection and sends FINS commands (e.g., Memory Read); the PLC responds with data.

Security and Best Practices

Pay attention to network and device security: segment your network, use secure management consoles, and keep firmware up-to-date. If you require remote access for maintenance or monitoring, consider a controlled remote access solution and ensure logging of sessions and changes.

When to Choose Host Link or FINS?

Choose Host Link if you are dealing with older PLCs or simple serial connections. Use FINS for modern installations with multiple participants, SCADA integration, and when you require more functions and a full address range.

Summary

Host Link is simple, ASCII-based, and suitable for serial connections. FINS is more powerful and designed for TCP/IP networks with extensive functions. The Omron memory model (CIO, W, H, DM, T/C, A) forms the basis for addressing and communication. With the correct parameters and addressing, PLCs, SCADA, and HMIs can efficiently exchange data over both serial lines and Ethernet.