Synchronous Idle

Symbol Meaning

The Synchronous Idle symbol is also known as the null symbol. It was used for synchronous data transmission in computer terminals, printers, text processing systems, and telecommunication equipment. The aim of this symbol was to synchronize data transmission between two devices. In synchronous communication protocols, the SYN symbol was applied to indicate the beginning and end of a block of data, allowing devices to correctly interpret and process the received information. Some communication lines were designed in such a way that they required continuous data transmission. Overall, Synchronous Idle was sent in case there was nothing to transmit.

As for modern computer systems and applications, the U+0016 symbol is rarely used there, since other mechanisms and protocols are employed to synchronize and process data.

Like many other control symbols, this one has no visible representation and doesn't occupy a lot of space on screen or in typed text. However, there is a separate symbol in Control Pictures2400–243F representing the graphical image of Synchronous Idle as the abbreviation SYN — .

The symbol “Synchronous Idle” is included in the “C0 controls” Subblock of the “Basic Latin” Block and was approved as part of Unicode version 1.1 in 1993.

Text is also available in the following languages: Русский;



Unicode Name Synchronous Idle
Unicode Number
CSS Code
Unicode Block Basic Latin
Unicode Subblock C0 controls
Unicode Version 1.1 (1993)
Keyboard shortcut ^V
Version 1.1
Block Basic Latin
Type of paired mirror bracket (bidi) None
Composition Exclusion No
Case change 0016
Simple case change 0016
Encoding hex dec (bytes) dec binary
UTF-8 16 22 22 00010110
UTF-16BE 00 16 0 22 22 00000000 00010110
UTF-16LE 16 00 22 0 5632 00010110 00000000
UTF-32BE 00 00 00 16 0 0 0 22 22 00000000 00000000 00000000 00010110
UTF-32LE 16 00 00 00 22 0 0 0 369098752 00010110 00000000 00000000 00000000