Perhaps, we lean a little too heavily on complicated UARTs and other peripheral chips everyone takes for granted. For low speed communications a UART really is not a necessary part of the hardware. Of course, different vendors implement various aspects of the standard in different ways, so devices hardly ever work together without some frantic wire swapping. RS-232 communications takes place one bit at a time. Each of the 8 bits of a byte are sequentially sent out over a single pair of wires.
All communications takes place at a baud rate agreed on by both the driver and receiver.
The receiver senses the start bit and sets itself up to read the incoming serialized byte. Data bits follow Start. One at a time, the other bits follow, each being given exactly one bit time on the link. After the entire character has been transferred the line goes to the marking state for the length of the stop bit - one or two bit times depending on the protocol agreed to by the communicating devices. Stop bits look like an idle line.