Hi,
How reliable can a UART be?
I'd say the microcontroller built in UART is at least the same reliable as any other interface.
But how reliable is the microcontroller, your software, the transmission line....
UART is just one small part of a communication. You need a physical interface also. Single TTL line maybe is the worst, then shielded TTL, then RS232, then RS485, then POF, then glass fiber ( just my opinion, i don't really know if this is the correct order..)
Then you need a protocol, parity, checksum, CRC ...
And the software for resending a packet.
If one packet relies on the other, ghen what about an accidental power fail, reset or any other issue....how do you re-sync your controllers?
Klaus