MODBUS is a request-response protocol used in Supervisory Control and Data Acquisition (SCADA) systems for industrial automation devices. It provides a simple open and standardized method for devices to communicate using a client/server model.

While initially deployed over RS232 interfaces, versions of the MODBUS protocol exist for serial lines (MODBUS RTU and MODBUS ASCII) and for Ethernet (MODBUS TCP). AlliedWare Plus™ supports the variant intended for use over Ethernet and IP networks, MODBUS TCP.

The MODBUS feature allows AlliedWare Plus devices to be used for some SCADA processes – such as gathering sensor and alarm information and to control and monitor the state of ports and their PoE state.