SOH
Start of Heading
ControlASCII 1 | Hex 0x01 | U+0001
SOH (code 1) marks the beginning of a message header in serial communication protocols. In the Kermit and BSC (Binary Synchronous Communication) protocols developed in the 1960s and 1970s, SOH told the receiver that addressing and routing information followed. Modern network protocols use structured packet headers instead, but SOH persists in some industrial automation protocols and barcode symbologies like GS1-128 where message framing still relies on ASCII control characters.
ASCII Code
Decimal
1
Hexadecimal
0x01
Octal
1
Binary
0000 0001
Unicode
Code Point
U+0001
Escape
\u0001
UTF-8 Hex
0xE2 0x90 0x81
UTF-8 Binary
111000101001000010000001
UTF-16
0x0001
UTF-32
0x00000001
HTML Entities
Numeric

Hex

How to Type
HTML Entity

Unicode InputU+0001
Source Code Representations
C / Java
"\u0001"CSS
\0001JavaScript
"\u0001"Perl
\x{0001}Python 2
u"\u0001"Python 3
\u0001Ruby
\u{0001}Frequently Asked Questions
What is ASCII code 1?
ASCII code 1 represents the Start of Heading character. In hexadecimal it is 0x01, in binary 0000 0001, and in octal 1. This is a non-printable control character used for device signaling and data transmission control.
How do I type ASCII 1 on a keyboard?
Control characters are typically entered using Ctrl key combinations. For example, Ctrl+A produces ASCII 1 in most terminal emulators. You can also use the HTML entity  in web pages.