A communication port used as a redundant link has the same channel The communications port used by the server to connect to a controller. Channels are one slot, point, or screw terminal of an I/O device for a single I/O value, and are defined using the Quick Builder tool. name but a requires a different port name to its twin. All other entries are identical to those of the primary 1. For Regulatory Control blocks in a cascade strategy: A primary is an upstream block from which an initializable input is fetched. A block has one primary for each initializable input. See also: block. 2. The controller (or chassis) that is currently controlling the redundant process by carrying out the assigned functions. Compare: secondary. See also: assigned function, chassis, controller redundancy. port.