According to here, UART is a hardware device that implement the asynchronous serial communication protocol.
And according to here, RS-232 defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors.
I think the UART alone is enough to determine the timing of the communication with start/stop bits.
And I saw below graph from here. It also shows only pin 2 and 3 of RS-232 are used by UART, which are merely for data RX and TX.
So,
How does the RS-232 circuit participate in the timing of async serial communication if it really does?
It seems to me UART only cares about 2 pins of RS-232. RS-232 was born long before UART. So it seems UART is essentially enabling the async serial communication on the good old RS-232 hardware by re-using the 2 pins of RS232 which happen to have the same semantic of Rx/Tx.
Is it appropriate to consider the UART IP as the logical part of the whole communication process and the RS-232 only as merely a conductor/carrier?
(inspired by @jonk's comment)
So when enabling UART on RS-232, we must consider the restrictions of RS-232. But if enable UART on other interfaces, a much faster bps may be achieved. So in this sense, RS-232 is somehow affecting the timing as well.
My point is, UART and RS-232 should be decoupled conceptually though I saw in many occasions they are used interchangeably.