OMRON NT-DRT21 DeviceNet Interface Unit for Programmable Terminals

The OMRON NT-DRT21 is a DeviceNet (CompoBus/D) interface unit designed to connect Omron NT-series Programmable Terminals to DeviceNet industrial networks. This interface unit serves as a communication gateway, enabling the PT to exchange data with PLCs, sensors, actuators, and other devices on the DeviceNet network. By integrating human-machine interface devices directly into the fieldbus network, the NT-DRT21 facilitates centralized monitoring and control of distributed automation systems while reducing wiring complexity compared to point-to-point connections.

Communication Capabilities

The NT-DRT21 Interface Unit supports both remote I/O communications and message communications, providing comprehensive flexibility for interacting with devices on the DeviceNet network. Remote I/O communications enable real-time exchange of I/O data between the Programmable Terminal and other network devices with predictable update rates. Message communications allow the PT to initiate explicit messaging for configuration, diagnostic retrieval, and on-demand data access, making the unit adaptable to both simple and complex network applications.

The unit is compatible with various NT-series Programmable Terminals including the NT31, NT31C, and other models supporting the DeviceNet interface option. The DeviceNet Interface Unit requires specific settings within the NT-series PT's system program, detailed in the PT Settings and Operations section of the interface unit operation manual. These settings configure the unit's DeviceNet node address, communication baud rate, and I/O assembly instances for proper network integration.

Power Consumption and Installation

The NT-DRT21 features low power consumption for efficient operation within industrial control systems. The internal operating power consumption is rated at 1 watt maximum, while the DeviceNet communications power consumption is 0.75 watt maximum, supplied separately from the DeviceNet network. This dual power architecture ensures that the interface unit remains operational even if the network communication power is disrupted, preserving PT functionality for local operations.

Installation of the NT-DRT21 involves mounting the unit to the compatible Programmable Terminal and connecting the DeviceNet network cable to the unit's communications port. The unit includes DIP switches or other configuration interfaces for setting the DeviceNet node address and communication parameters. Proper termination of the DeviceNet trunk line and conformance to network topology rules are essential for reliable communication.

DeviceNet Network Integration

The NT-DRT21 operates as a DeviceNet slave device, responding to I/O polling and explicit message requests from a DeviceNet master such as an Omron CJ2M-CPU3x with built-in DeviceNet port or a C200HW-DRT21 interface module. The DeviceNet protocol, based on CAN technology, provides robust communication with built-in error detection, collision avoidance, and deterministic message delivery. The network supports baud rates of 125 kbps, 250 kbps, and 500 kbps, with cable lengths up to 500 meters depending on baud rate selection.

The DeviceNet Interface Unit allows the Programmable Terminal to access data from any DeviceNet device, enabling features such as displaying real-time production data from PLC registers, acknowledging alarms from remote I/O stations, and initiating control actions from touch-screen inputs. The PT can read and write data to DeviceNet devices using standard DeviceNet object model addressing, simplifying application programming compared to proprietary communication protocols.

Configuration and Operation

Configuration of the NT-DRT21 requires both hardware switch settings and software configuration within the PT's application program. The interface unit operation manual provides detailed procedures for installation, parameter setting, and troubleshooting. Refer to the DeviceNet operation manual for overall network details and configuration of other network devices.

The unit includes status indicators for network power, communication activity, and error conditions, enabling rapid diagnostics during installation and maintenance. When properly configured, the NT-DRT21 operates transparently, passing data between the PT and DeviceNet network without requiring user intervention. The interface unit supports firmware updates and diagnostic data retrieval through the DeviceNet network when supported by the master device, simplifying maintenance across large installations.

The OMRON NT-DRT21 is essential for applications requiring operator interface devices at multiple points on a DeviceNet network, including packaging lines, material handling systems, assembly stations, and process control skids. By enabling PTs to communicate directly over DeviceNet, the unit eliminates dedicated communication wiring between each PT and the PLC, reducing installation costs and simplifying system expansion.