The Rockwell module you mentioned, 1784-PCD1, is a part of the Allen-Bradley 1784-PCD series. The 1784-PCD1 is a communication module used for connecting a personal computer (PC) to a ControlNet network. It provides the interface between the PC and the network, allowing data exchange and communication between the PC and other devices on the ControlNet network.

This module is designed to be used with the Rockwell Automation ControlLogix programmable automation controllers (PAC) and is typically used in industrial automation applications. It supports high-speed data transfer rates and offers reliable network connectivity.