MODBUS TCP is an open industry standard widely spread due to its ease of use. It is a request response protocol and offers services specified by function codes.

MODBUS TCP combines the MODBUS RTU with standard Ethernet and universal networking standard TCP. It is an application-layer messaging protocol, positioned at level 7 of the OSI model. The CI867/TP867 is used for connection between an AC 800M controller and external Ethernet devices using Modbus TCP protocol.

The CI867 expansion unit contains the CEX-Bus logic, a communication unit and a DC/DC converter that supplies appropriate voltages from the +24 V supply via the CEX-Bus. The Ethernet cable must be connected to the main network through an Ethernet switch.