SELF-CLOCKING SIGNAL

In telecommunications and electronics, a 'self-clocking signal' is one that can be decoded without the need for a separate clock signal or other source of synchronization. This is usually done by including embedded synchronization information within the signal, and adding constraints on the coding of the data payload such that false synchronization can easily be detected.
Most line codes are designed to be self-clocking.
Examples of self-clocking signals include:
Isochronous:

★ Manchester code. The clock signals occur at the transition points.

★ PDH signals

★ Eight-to-Fourteen Modulation

★ 4B5B

★ 8B/10B encoding

★ HDLC

★ Modified Frequency Modulation
Anisochronous:

★ Morse code

★ Asynchronous start-stop
Most of these codes can be seen as a kind of Run Length Limited code. Those constraints on "runs" of zeros and "runs" of ones ensure that transitions occur often enough to keep the receiver synchronized.