USART question - start/stop bits

[rezaxyz]

USART question

Hi dear friends,
I am interested to know why a character must be framed by start and stop bits in USART's synchronous mode, despite the receiver can be synchronized with transmitter by an external clock line.

Thank in advance,
Reza

 

[FvM]

Re: USART question

Generally, synchronous serial transmission does not use start/stop framing. Some variants, also named sychronous, may use it. You need, however, some means of frame synchronisation, e. g. a HDLC protocol. To my opinion, it's rather vague to talk of synchronous transmission as such, for clarity, you should specify a particular protocol.