The first 32 codes (0 to 31) and the final code (127) in the standard ASCII table are designated as control characters or non-printable characters.
These codes were originally developed to control hardware devices like teleprinters, instructing them to perform actions such as advancing a line, sounding a bell, or managing transmission links rather than displaying visible text.
| Dec | Hex | Oct | Bin | HTML Code |
Abbr | Description |
|---|---|---|---|---|---|---|
| 0 | 00 | 000 | 00000000 | � | NUL | Null |
| 1 | 01 | 001 | 00000001 |  | SOH | Start of Heading |
| 2 | 02 | 002 | 00000010 |  | STX | Start of Text |
| 3 | 03 | 003 | 00000011 |  | ETX | End of Text |
| 4 | 04 | 004 | 00000100 |  | EOT | End of Transmission |
| 5 | 05 | 005 | 00000101 |  | ENQ | Enquiry |
| 6 | 06 | 006 | 00000110 |  | ACK | Acknowledge |
| 7 | 07 | 007 | 00000111 |  | BEL | Bell |
| 8 | 08 | 010 | 00001000 |  | BS | Backspace |
| 9 | 09 | 011 | 00001001 | 	 | HT | Horizontal Tab |
| 10 | 0A | 012 | 00001010 | | LF | Line Feed (New Line) |
| 11 | 0B | 013 | 00001011 |  | VT | Vertical Tab |
| 12 | 0C | 014 | 00001100 |  | FF | Form Feed (New Page) |
| 13 | 0D | 015 | 00001101 | | CR | Carriage Return |
| 14 | 0E | 016 | 00001110 |  | SO | Shift Out |
| 15 | 0F | 017 | 00001111 |  | SI | Shift In |
| 16 | 10 | 020 | 00010000 |  | DLE | Data Link Escape |
| 17 | 11 | 021 | 00010001 |  | DC1 | Device Control 1 (XON) |
| 18 | 12 | 022 | 00010010 |  | DC2 | Device Control 2 |
| 19 | 13 | 023 | 00010011 |  | DC3 | Device Control 3 (XOFF) |
| 20 | 14 | 024 | 00010100 |  | DC4 | Device Control 4 |
| 21 | 15 | 025 | 00010101 |  | NAK | Negative Acknowledge |
| 22 | 16 | 026 | 00010110 |  | SYN | Synchronous Idle |
| 23 | 17 | 027 | 00010111 |  | ETB | End of Transmission Block |
| 24 | 18 | 030 | 00011000 |  | CAN | Cancel |
| 25 | 19 | 031 | 00011001 |  | EM | End of Medium |
| 26 | 1A | 032 | 00011010 |  | SUB | Substitute |
| 27 | 1B | 033 | 00011011 |  | ESC | Escape |
| 28 | 1C | 034 | 00011100 |  | FS | File Separator |
| 29 | 1D | 035 | 00011101 |  | GS | Group Separator |
| 30 | 1E | 036 | 00011110 |  | RS | Record Separator |
| 31 | 1F | 037 | 00011111 |  | US | Unit Separator |
| 127 | 7F | 177 | 01111111 |  | DEL | Delete |