Comparison of synchronous and asynchronous signalling

The receiver uses transitions on that signal to figure out the transmitter bit rate ("autobaud") and timing, and set a local clock to the proper timing, typically using a phase-locked loop (PLL) to synchronize with the transmission rate.

In synchronous communications, the stream of data to be transferred is encoded as fluctuating voltage levels in one wire (the 'DATA'), and a periodic pulse of voltage on a separate wire (called the "CLOCK" or "STROBE") which tells the receiver "the current DATA bit is 'valid' at this moment in time".

Practically all parallel communications protocols use synchronous transmission.

The word structure used in typical asynchronous serial communications is START-DATA[0:7]-PARITY[optional;0]-STOP[0:1].

These formatting variables are specified when configuring the transmit and receive nodes before communications take place.