The stub cables are for bi-directional data movement between LRU and current mode coupler. The stub cables also supply power from the LRUs to the current couplers. The stub cable has four wires, two to transmit and two to receive. These cables are in the normal aircraft wiring bundles.
Figure shows the basic layout for connecting LRUs to the 629 data bus using stub cables. The stub cable length is up to 50ft for TX/RX cable and 75ft for RX only cable.