In a building automation network, a multipoint communication in RS-485 refers to which scenario?

• A. Communication among more than two devices
• B. One-to-one communication
• C. Wireless only
• D. Fiber-only bus

Answer: (A)

Multipoint on RS-485 means several devices share the same two-wire differential bus. This lets a single RS-485 network connect many controllers, sensors, or actuators on the same pair of wires, rather than having a separate link between just two devices. On the bus, data is driven by one device at a time (usually in half‑duplex mode), while all other devices listen and can respond when addressed. Proper bus design uses end-of-line terminations and biasing to keep signals clean over long distances.

That’s why this scenario fits multipoint: there’s communication among more than two devices on the same RS-485 network. The other options don’t fit because RS-485 is a wired, multi-point standard (not wireless only or fiber-only) and it isn’t limited to just a one-to-one link.