How to connect multiple devices to UART bus?
UART protocol is normally used on point-to-point links, and does not define a "bus" as such.

You can use UART protocol on a bus, but you must also define an electrical interface that allows this to occur correctly. In a master-slave arrangement, the primary issue is controlling which slave drives the master's receive input. You could use an open-collector arrangment, a matrix of diodes, or some kind of active multiplexer.