Kode ASCII, BCD, BCDIC, EBCDIC, BAUDOT

ASCII Kode
Kode Standar Amerika untuk Pertukaran Informasi atau ASCII (American Standard Code for Information Interchange) merupakan suatu standar internasional dalam kode huruf dan simbol seperti Hex dan Unicode tetapi ASCII lebih bersifat universal, contohnya 124 adalah untuk karakter "|". Ia selalu digunakan oleh komputer dan alat komunikasi lain untuk menunjukkan teks. Kode ASCII sebenarnya memiliki komposisi bilangan biner sebanyak 8 bit. Dimulai dari 0000 0000 hingga 1111 1111. Total kombinasi yang dihasilkan sebanyak 256, dimulai dari kode 0 hingga 255 dalam sistem bilangan Desimal.

BCD Kode

Binary Coded Decimal (BCD or "8421" BCD) numbers are made up using just 4 data bits (a nibble or half a byte) similar to the Hexadecimal numbers we saw in the binary tutorial, but unlike hexadecimal numbers that range in full from 0 through to F, BCD numbers only range from 0 to 9, with the binary number patterns of 1010 through to 1111 (A to F) being invalid inputs for this type of display and so are not used as shown below.

Decimal Binary Pattern BCD 8 4 2 1 0 0 0 0 0 0 1 0 0 0 1 1 2 0 0 1 0 2 3 0 0 1 1 3 4 0 1 0 0 4 5 0 1 0 1 5 6 0 1 1 0 6 7 0 1 1 1 7

Decimal Binary Pattern BCD 8 4 2 1 8 1 0 0 0 8 9 1 0 0 1 9 10 1 0 1 0 Invalid 11 1 0 1 1 Invalid 12 1 1 0 0 Invalid 13 1 1 0 1 Invalid 14 1 1 1 0 Invalid 15 1 1 1 1 Invalid

BCD to 7-Segment Display Decoders

A binary coded decimal (BCD) to 7-segment display decoder such as the TTL 74LS47 or 74LS48, have 4 BCD inputs and 7 output lines, one for each LED segment. This allows a smaller 4-bit binary number (half a byte) to be used to display all the denary numbers from 0 to 9 and by adding two displays together, a full range of numbers from 00 to 99 can be displayed with just a single byte of 8 data bits.

BCD to 7-Segment Decoder

The use of packed BCD allows two BCD digits to be stored within a single byte (8-bits) of data, allowing a single data byte to hold a BCD number in the range of 00 to 99.

An example of the 4-bit BCD input (0100) representing the number 4 is given below.

Example No1

In practice current limiting resistors of about 150Ω to 220Ω would be connected in series between the decoder/driver chip and each LED display segment to limit the maximum current flow. Different display decoders or drivers are available for the different types of display available, e.g. 74LS48 for common-cathode LED types, 74LS47 for common-anode LED types, or the CMOS CD4543 for liquid crystal display (LCD) types.

Liquid crystal displays (LCD´s) have one major advantage over similar LED types in that they consume much less power and nowadays, both LCD and LED displays are combined together to form larger Dot-Matrix Alphanumeric type displays which can show letters and characters as well as numbers in standard Red or Tri-colour outputs.

BCDIC Kode

EBCDIC Kode  
ASCII is not the only format in use out there. IBM adopted EBCDIC (Extended Binary Coded Decimal Interchange Code) developed for punched cards in the early 1960s and still uses it on mainframes today. It is probably the next most well known character set due to the proliferation of IBM mainframes. It comes in at least six slightly differing forms, so again here is the most common. 

BAUDOT Kode

This table presents a programmer's quick reference to the "Baudot" character set.

IMPORTANT NOTE: The code presented here is with reference to usage in the computer industry. The original, true, baudot code differs from that presented below. The following table presents CCITT Alphabet No 2 which was developed from Murray's code which was in turn developed from Baudot's code. Baudot's code was replaced by Murray's code in 1901. And ITA2 replaced both by the early 1930's, so virtually all "teletype" equipment made in the U.S. uses ITA2 or the U.S. national version of the code.

The 'baudot' code has been used extensively in telegraph systems. It is a five bit code invented by the Frenchman Emile Baudot in 1870. Using five bits allowed 32 different characters. To accomodate all the letters of the alphabet and numerals, two of the 32 combinations were used to select alternate character sets. The figures column is valid after a figures shift character has been received. It remains in effect until a letters shift is received, after which the letters column should be referred to (and vice-versa).

Two 'Baudot codes' are in common useage. The first as used in America. The second, used in Europe, is also termed the CCITT Alphabet No. 2. In each, the 'letters' are identical, but the 'figures' differ.

The five-bit words are bracketed by a start bit (space) and a stop bit (mark). Idling is shown by the 'marking' state. Words are transmitted LSB first.

Binary	Decimal	Hex	Octal	Letter	U.S. Figures	CCITT No.2 Figures
00000	0	0	0	N/A	N/A	N/A
00001	1	1	1	E	3	3
00010	2	2	2	LF	LF	LF
00011	3	3	3	A	-	-
00100	4	4	4	Space	Space	Space
00101	5	5	5	S	BELL	'
00110	6	6	6	I	8	8
00111	7	7	7	U	7	7
01000	8	8	10	CR	CR	CR
01001	9	9	11	D	$	WRU
01010	10	A	12	R	4	4
01011	11	B	13	J	'	Bell
01100	12	C	14	N	,	,
01101	13	D	15	F	!	!
01110	14	E	16	C	:	:
01111	15	F	17	K	(	(
10000	16	10	20	T	5	5
10001	17	11	21	Z	"	+
10010	18	12	22	L	)	)
10011	19	13	23	W	2	2
10100	20	14	24	H	#	£
10101	21	15	25	Y	6	6
10110	22	16	26	P	0	0
10111	23	17	27	Q	1	1
11000	24	18	30	O	9	9
11001	25	19	31	B	?	?
11010	26	1A	32	G	&	&
11011	27	1B	33	Figures Shift	Figures Shift	Figures Shift
11100	28	1C	34	M	.	.
11101	29	1D	35	X	/	/
11110	30	1E	36	V	;	=
11111	31	1F	37	Letters Shift	Letters Shift	Letters Shift

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