Allen Bradley 1756-DHRIO ControlLogix Communication Module The 1756-DHRIO is an Allen-Bradley communication module that support Remote I/O and Data Highway Plus (DH) protocol. This module has embedded Two (2) ports for Channel A and B each with a with 3-Pin terminal for wiring Data Highway Plus (DH+) or Remote I/O (RIO) and a single 8-Pin mini-DIN port that is connected parallel to Channel A.