Multidrop

Multidrop is a term used in communications engineering to describe a topology where multiple devices share a single transmission medium. In a multidrop network, many nodes attach to the same wire pair so that signals propagate along the line and messages include addressing so that only the intended recipient processes them. This approach is common in industrial and embedded systems and is typically implemented with master-slave or multi-master protocols.

Common examples include RS-485 and CAN bus networks. RS-485 is a differential two-wire bus that supports multi-point connections; the traditional standard supports up to about 32 devices on a bus, with repeaters enabling larger installations. CAN bus is a multi-master bus with built-in arbitration, widely used in automotive and industrial contexts. Both rely on careful physical layer design, including termination resistors at the ends, biasing to define the idle state, and impedance control. Topologies are typically linear or daisy-chained; star configurations are generally avoided because they can cause reflections and impedance mismatches.

Key design considerations include addressing schemes, arbitration or polling to avoid collisions, bus loading, cable length, and fault management. The term multidrop is sometimes used interchangeably with multipoint or bus, though some standards reserve multidrop for specific implementations. See also multipoint communication and bus topology.