Is serial port asynchronous?

Using Arduino Project Guidance
1

Greetings All!

I'm wondering whether serial port is asynchronous or synchronous?

For example if I need to do UART/Serial port communication with two MCUs, and the second MCU would be started later, so their clocks are not in sync. When I send a byte from A to B, would second MCU still get the correct data if the clock was out of sync? Do they rely on fixed time intervals between one bit to the another?

For example if I think about SPI, there is always the clock signal which tells everyone in the line that hey I'm now transfering the beginning of the bit. Does UART/Serial port have start and end bits to notify the second MCU that "hey you, I'm beginning to transfer now, please sync the clock!"

How is it with serial port? Can I communicate from one MCU to another MCU without external syncing?

Thanks!

2

Google "UART" - you'll get your answer.
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Guess you found it.
The serial comm is based on a speed agreed before comm begins.
Serial.begin(speed);
The sender sends a start bit (to tell reveiver that a byte is following)
Then 8 bits , (a parity bit if this is part of agreement) and at last minimun 1 stop bit (where line 'rests')
Serial.write(byte);
You can pause for an undefined time before sending the next byte.

3

yes, asynchronous
yes, start bit and stop bit
both stations run the same baudrate

yes, google that

4

Great, thanks!