Multi-channel analog/digital multiplexer is a bi-directional, fiber optic multiplexer. It can be used to send and receive up to 8 channels of electrical interface information over a pair of fiber optic cables. It is used for contact closure applications. The base unit connects to the fiber optic cable and provides visual indication of fiber link status. The information is received from up to four input modules that can be cascaded. Each module has a partner module installed on the corresponding base unit. An integrated back plane allows for communications between modules with no external inter-modular connection.