Code 2

1. About the code

Only by arranging whether electricity flows (1) or does not flow (0) on the computer, people feel uncomfortable with the expression of the number system or language used in real life. Therefore, a promise is made to have a certain meaning for a specific binary sequence, which is collectively called a code.
  Although there is no separate standard, it can be divided into two main categories: codes for reducing or checking errors in computer devices, and codes for comfortable writing of numbers and characters. There are more types of codes than the ones below, but let's look at only a few codes for the convenience of people.

 

2. 8421 code

Humans use decimal numbers by default, but computers use binary numbers by default, so readability is poor. In particular, it is inconvenient to convert whenever the number of digits of decimal notation increases or whenever a decimal representation other than the decimal system such as date/time is used.
  For this reason, 4 binary digits are allocated to each decimal number, and 10 fixed arrays corresponding to 0₁₀ to 9₁₀ are used, other expressible arrays are not used. This code is called BCD (Binary Coded Decimal). BCD includes 8421 code, excess-3 code, 2421 code, 5421 code, 51111 code (5 binary digits), etc. Among them, 8421 codes are used as representative.
  The 8421 code gives weights of 8, 4, 2, and 1 to each of the 4 binary digits, and the correspondence with the decimal number is the same as that of the basic binary number. If we change the decimal number 169₁₀ to the 8421 code, it is as follows.

 

Decimal	1				2				7
Weight	8	4	2	1	8	4	2	1	8	4	2	1
8421 code	0	0	0	1	0	0	1	0	0	1	1	0

 

Assign a decimal number to 4 binary digits for each digit, and place the weights in order so that the sum of the decimal and binary numbers is equal. For decimal numbers 0₁₀ to 9₁₀, only binary numbers 0000₂ to 1001₂ are supported, so it is not used for the rest of 1010₂ to 1111₂.
  There is a difference in the number of digits between the 8421 code and the general binary number, so when converted to binary like 127₁₀, even if the binary number ends with 7 digits, the 8421 code allocates 12 digits and is often used unnecessarily. In addition, 6 digits are empty between 9₁₀ and 10₁₀, so be careful when performing arithmetic operations.

 

3. ASCII

Human numbers can be used in correspondence with binary numbers, but since computers do not have the concept of characters, it is possible to express words or sentences only by matching the entire character system. In the United States, in 1963, a code was created to correspond to 7 binary digits by combining punctuation marks, numbers, uppercase and lowercase of Roman characters (Latin characters), this is called ASCII (American Standard Code for Information Interchange). It is used all over the world to the extent that it is used as a standard for information transmission by adding 1 digit of parity for error checking to 7 digits of ASCII.
  Besides ASCII, there is an EBCDIC(Extended Binary Coded Decimal Interchange Code) that is extended from BCD to express characters, but it is an 8-digit code, with more inconspicuous symbols and due to the inconvenience of using ASCII, so it is not used as well as ASCII.
  The table below is the known ASCII correspondence table. (The corresponding binary number is long, so it is replaced with a hexadecimal number.)

 

Dec	Hex	Char	Dec	Hex	Char	Dec	Hex	Char	Dec	Hex	Char
010	0016	NUL	3210	2016	Space	6410	4016	@	9610	6016	`
110	0116	SOH	3310	2116	!	6510	4116	A	9710	6116	a
210	0216	STX	3410	2216	“	6610	4216	B	9810	6216	b
310	0316	ETX	3510	2316	#	6710	4316	C	9910	6316	c
410	0416	EOT	3610	2416	$	6810	4416	D	10010	6416	d
510	0516	ENQ	3710	2516	%	6910	4516	E	10110	6516	e
610	0616	ACK	3810	2616	&	7010	4616	F	10210	6616	f
710	0716	BEL	3910	2716	‘	7110	4716	G	10310	6716	g
810	0816	BS	4010	2816	(	7210	4816	H	10410	6816	h
910	0916	TAB	4110	2916	)	7310	4916	I	10510	6916	i
1010	0A16	LF	4210	2A16	*	7410	4A16	J	10610	6A16	j
1110	0B16	VT	4310	2B16	+	7510	4B16	K	10710	6B16	k
1210	0C16	FF	4410	2C16	,	7610	4C16	L	10810	6C16	l
1310	0D16	CR	4510	2D16	-	7710	4D16	M	10910	6D16	m
1410	0E16	SO	4610	2E16	.	7810	4E16	N	11010	6E16	n
1510	0F16	SI	4710	2F16	/	7910	4F16	O	11110	6F16	o
1610	1016	DLE	4810	3016	0	8010	5016	P	11210	7016	p
1710	1116	DC1	4910	3116	1	8110	5116	Q	11310	7116	q
1810	1216	DC2	5010	3216	2	8210	5216	R	11410	7216	r
1910	1316	DC3	5110	3316	3	8310	5316	S	11510	7316	s
2010	1416	DC4	5210	3416	4	8410	5416	T	11610	7416	t
2110	1516	NAK	5310	3516	5	8510	5516	U	11710	7516	u
2210	1616	SYN	5410	3616	6	8610	5616	V	11810	7616	v
2310	1716	ETB	5510	3716	7	8710	5716	W	11910	7716	w
2410	1816	CAN	5610	3816	8	8810	5816	X	12010	7816	x
2510	1916	EM	5710	3916	9	8910	5916	Y	12110	7916	y
2610	1A16	SUB	5810	3A16	:	9010	5A16	Z	12210	7A16	z
2710	1B16	ESC	5910	3B16	;	9110	5B16	[	12310	7B16	{
2810	1C16	FS	6010	3C16	<	9210	5C16	＼	12410	7C16	|
2910	1D16	GS	6110	3D16	=	9310	5D16	]	12510	7D16	}
3010	1E16	RS	6210	3E16	>	9410	5E16	^	12610	7E16	~
3110	1F16	US	6310	3F16	?	9510	5F16	_	12710	7F16	DEL

 

In this table, 0₁₀(00₁₆) to 31₁₀(1F₁₆) and 127₁₀(7F₁₆) are called control characters and are not symbols representing actual characters. Excluding this control character, it consists of 10 numbers from 48₁₀(30₁₆), 26 uppercase letters from 65₁₀(41₁₆), 26 lowercase letters from 97₁₀(61₁₆), and the rest of the punctuation marks. Using these letters, numbers, and symbols, it is possible to express words, sentences, and numbers.

 

4. Unicode

As ASCII is used worldwide, characters of each country are also assigned to codes by adding digits(128₁₀(80₁₆)~) based on ASCII as needed. However, if an independently created character sequence is exchanged globally, there is no way to be compatible. Accordingly, in 1991, a coding system that handles all characters in the world was created and announced, which is Unicode (Unique, Universal, and Uniform character encoding).
  The purpose of the code can be seen from the name, and characters from the past, including modern ones, are continuously being added with the goal of fully expressing all writing systems. If ASCII is 128 characters with 7 binary digits, Unicode has 21 binary digits, and the number of possible codes exceeds 1 million characters. Even after allocating characters used up to the present time, there is room for symbols, so pictures, emoticons, and game symbols are sometimes added.
  In the Unicode system, symbols are expressed using 4 to 6 hexadecimal digits as a prefix with U+. Here are a few examples that are actually used:

 

From U+0020 to U+007F (127 characters): Basic Latin (same content as ASCII)

From U+0250 to U+02AF (96 characters): IPA Extensions

From U+0370 to U+03FF (135 characters): Greek

From U+3131 to U+318E (94 characters): Hangul Compatibility Jamo

From U+AC00 to U+D7A3 (11252 characters): Hangul Syllables

From U+1F300 to U+1F5FF (768 characters): Miscellaneous Symbols and Pictographs

From U+1F600 to U+1F64F (80 characters): Emoticons

 

Characters written in 4 hexadecimal digits belong to the Basic Multilingual Plane(BMP, U+0000~U+FFFF), and most of the characters used today fall into this category. In addition, there are Supplementary Multilingual Plane(SMP, 10000~1FFFF), Supplementary Ideographic Plane(SIP, U+20000~2FFFF), and Tertiary Ideographic Plane(TIP, U+30000~3FFFF). Supplementary multilingual is rarely used, and most of the ideograms are assigned Chinese characters as symbols.

If you visit https://www.unicode.org/roadmaps/bmp/index.html, you can check all currently used characters. This makes it possible to read and write all characters equally around the world just by-passing information arranged in binary.

 

5. Conclusion

Know only the type of code, and if necessary, find a table on the Internet and use it.