Four Column ASCII Table:

Notes:

• In a four column ASCII table, the 32 characters on the first column of the table don't represent a written symbol: these characters such as Backspace, Newline, Escape, etc. are called control characters.

• In the terminal, you can type these control characters by holding the CTRL key in combination with another key (mnemonic: use a CTRL key combination for control characters).

  • In the VIM editor, for example, pressing CTRL + [ in the terminal (which is ^[ in caret notation) is the same as pressing the ESC key. The character [ and ESC are on the same row in a four column ASCII table (fifth row from bottom).

  • You might be wondering why pressing CTRL + [ yields ESC and not other characters on the same row such as ; and {. That's because pressing CTRL simply sets all bits but the last 5 to zero in the 7 bit ASCII for the character that you typed (i.e. the first two bits is set to zero and the last 5 bits remain the same). In essence, the CTRL character serves as the "bitwise AND": the result is 1 only if both operands are 1.

      10 11011 ([)
    & 00 11111 (CTRL)
    = 00 11011 (ESC)
    

• When the ASCII table is printed in rows of 32, looking up data becomes easier:

  • Upper case and lower case alphabet differs by only a single bit (e.g. 10 00001 => A and 11 00001 => a).

  • The character for the CTRL keyboard combination and the corresponding control character all exists on the same row. For example, the key combination CTRL + [ corresponds to ESC in the same row (fifth row from bottom).

ASCII is a 7 bit encoding:

• The first two bits denote the group of the character (2^2 so 4 possible values)

• The remaining five bits describe a character (2^5 so 32 possible values)

00	01	10	11
NUL	Spc	@	`	00000
SOH	!	A	a	00001
STX	"	B	b	00010
ETX	#	C	c	00011
EOT	$	D	d	00100
ENQ	%	E	e	00101
ACK	&	F	f	00110
BEL	'	G	g	00111
BS	(	H	h	01000
TAB	)	I	i	01001
LF	*	J	j	01010
VT	+	K	k	01011
FF	,	L	L	01100
CR	-	M	m	01101
SO	.	N	n	01110
SI	/	O	o	01111
DLE	0	P	p	10000
DC1	1	Q	q	10001
DC2	2	R	r	10010
DC3	3	S	s	10011
DC4	4	T	t	10100
NAK	5	U	u	10101
SYN	6	V	v	10110
ETB	7	W	w	10111
CAN	8	X	x	11000
EM	9	Y	y	11001
SUB	:	Z	z	11010
ESC	;	[	{	11011
FS	<	\	|	11100
GS	=	]	}	11101
RS	>	^	~	11110
US	?	_	DEL	11111

References

1. Four Column ASCII