RS-485 has a shared bus but differs from SPI. In an RS-485 network, all devices share the same 2 wires labeled A and B. Each device has an RS-485 transceiver that manages communication with the bus and can be controlled by the processor of the host system. In most cases the host system may use serial UART to talk to the RS-485 transceiver, where the host tells the transceiver when to talk and when to listen. Because all devices share the same bus, each device must have its own unique node address. The host will put its transceiver in transmit mode, and then send the node address. Immediately after this will put the transceiver in receive mode and listen for the response. Only one device can control the bus at a time which is why the transceiver must not change modes. The bottom image illustrates what a position request looks like with the AMT21 absolute RS-485 encoder series. A and B are the complementary pairs. The host controls the bus by sending the node address 0x54 to an encoder on the bus and within microseconds that encoder responds with its current position.