Synchronous Idle is the ASCII

ASCII

The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...

 control character

Control character

In computing and telecommunication, a control character or non-printing character is a code point in a character set, that does not in itself represent a written symbol.It is in-band signaling in the context of character encoding....

 22 (0x16), represented as ^V in caret notation

Caret notation

Caret notation is a notation for unprintable control characters in ASCII encoding. The notation consists of a caret followed by a capital letter; this digraph stands for the ASCII code that has the numerical value equivalent to the letter's numerical value. For example the EOT character with a...

. Synchronous Idle is used in some synchronous serial communication systems such as Teletype

Teletype Corporation

The Teletype Corporation, a part of American Telephone and Telegraph Company's Western Electric manufacturing arm since 1930, came into being in 1928 when the Morkrum-Kleinschmidt Company changed its name to the name of its trademark equipment...

 machines or the bisync protocol to provide a signal from which synchronous correction may be achieved between data terminal equipment, particularly when no other character is being transmitted.

The SYN character has the bit pattern 00010110, which has the property that it is distinct from any bit-wise rotation of itself. This helps bit-alignment of sequences of synchronous idles.