The Allen-Bradley 1756-A13 is ControlLogix chassis. This hardware provides Thirteen (13) module mounting slots, hosting the ControlLogix modules and enables backplane connectivity. This chassis has a maximum backplane current of 1.5 A @ 1.2VDC; 4A/4A @ 3.3 VDC; 15 A/6 A @ 15 A/6 A and 2.8 A/2.8 A @ 24VDC. It supports horizontal mounting with minimum cabinet size requirement of 60.9 x 76.2 x 20.3 cm (24 x 30 x 8 in.).
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.