RS485 control module RBT20

Product information
The romutec RBT20 control module provides four switches (Auto - Off - Hand 1 - Hand 2) to command or manually override four digital outputs located on a DDC or other connected fieldbus devices. Digital outputs are driven by bus commands over a Modbus connection and can be used to control 1- or 2-stage actuators, valves or similar actuators. The module features eight LEDs to signal operational and fault messages (for example frost, filter, drive belt) and status messages such as damper positions. LED colors are red, green and orange. An LED lamp test can be triggered via bus command or locally using the lamp test pushbutton on the module. A dedicated register reports whether and which switch was moved since the last read; reading the register resets all bits. Multiple position changes between reads are still reported as a change. For system configuration (addressing, maximum number of modules per Modbus master, mounting, bus connection), refer to the Configuration chapter.

Characteristics / Specifications

• Model: RBT20
• Function: Control module with 4 switches (Auto / Off / Hand 1 / Hand 2) for driving or manually overriding 4 digital outputs
• Interface: Modbus (bus commands to control digital outputs and LEDs)
• Digital outputs: 4 DO, suitable for 1- or 2-stage actuators
• LED indications: 8 messages (operation, faults such as frost, filter, drive belt; status messages such as damper positions). LED colors: Red, Green, Orange
• Lamp test: via bus command or local lamp test pushbutton
• Switch query: register indicates if/which switch moved since last read; reading resets bits
• System integration note: Addressing, maximum modules per Modbus master, mounting and bus connection as per Configuration chapter
• Manufacturer: romutec Steuer- und Regelsysteme GmbH
• SKU: 00003001
• Weight: 0.081 kg
• Release date: 2026-04-28

Integration and installation
Configure Modbus addressing and wiring according to the Configuration chapter. Observe limits on the number of modules per Modbus master and follow the mounting instructions to ensure reliable bus communication and signal integrity.

Typical applications

• Manual or remote control of 1- or 2-stage actuators
• Control of fans, valves and dampers
• Status indication and fault signalling via LEDs