BCD (6-bit)

Six-bit BCD code (Binary-Coded Decimal), alphanumeric BCD, alphameric BCD, BCD Interchange Code, or BCDIC is a representation of numerals, uppercase Latin letters, and some special and control characters as a six-bit character code. Unlike later encodings such as ASCII, BCD codes were not standardized. Different computer manufacturers, and even different product lines of the same manufacturer, often had their own variants, and sometimes included unique characters.

With the introduction of the IBM Card in 1928, IBM created a code capable of representing alphanumeric information, later adopted by other manufacturers. The six-bit BCD code was the adaptation of the punched card code to binary code.

Among the vendors using six-bit BCD were: Burroughs, Bull, CDC, IBM, General Electric, NCR, Siemens, Sperry - Univac, etc.

BCD code variations

There are different versions of the six-bit BCD code. There are at least 4 versions with some different characters, and others with a completely different mapping such as BCD code "FIELDATA".

None of the variations (nor the original) have room for control characters, 0x20 is the space character. In "Spanish speaking countries", the character "Ñ" did not exist in the original system, therefore "@" was chosen by most manufacturers: Bull, NCR, and Control Data, but there was an inconsistency when merging databases to 7-bit ASCII code, for in "that coding system" the "/" character was chosen resulting in two different codes for the same character.

GBCD code

Below is the table of GBCD code, a variant of BCD code.

Numbers (coded with binary value 0-9), capital letters A through Z, a minimum of symbols and no control character.
To emulate control character some symbols got special meaning like #,?,! when followed by e.g. a number. CR/LF is '!1', FF='! ' etc.

	000	001	002	003	004	005	006	007
000	0	1	2	3	4	5	6	7
001	8	9	[	#	@	:	>	?
002		A	B	C	D	E	F	G
003	H	I	&	.	]	(	<	\
004	^	J	K	L	M	N	O	P
005	Q	R	-	$	*	)	;	'
006	`	/	S	T	U	V	W	X
007	Y	Z	<	,	%	=	"	!
	000	001	002	003	004	005	006	007

Binary map of GBCD code

Numbers (coded with binary value 0-9), capital letters A through Z, a minimum of symbols and no control characters.


0 - 00- 0 0 0 0 0 0
1 - 01- 0 0 0 0 0 1
2 - 02- 0 0 0 0 1 0
3 - 03- 0 0 0 0 1 1
4 - 04- 0 0 0 1 0 0
5 - 05- 0 0 0 1 0 1
6 - 06- 0 0 0 1 1 0
7 - 07- 0 0 0 1 1 1
8 - 10- 0 0 1 0 0 0
9 - 11- 0 0 1 0 0 1
[ - 12- 0 0 1 0 1 0
# - 13- 0 0 1 0 1 1
@ - 14- 0 0 1 1 0 0
: - 15- 0 0 1 1 0 1
> - 16- 0 0 1 1 1 0 (= >)
? - 17- 0 0 1 1 1 1
_ - 20- 0 1 0 0 0 0 (space)
A - 21- 0 1 0 0 0 1
B - 22- 0 1 0 0 1 0
C - 23- 0 1 0 0 1 1
D - 24- 0 1 0 1 0 0
E - 25- 0 1 0 1 0 1
F - 26- 0 1 0 1 1 0
G - 27- 0 1 0 1 1 1
H - 30- 0 1 1 0 0 0
I - 31- 0 1 1 0 0 1
& - 32- 0 1 1 0 1 0
. - 33- 0 1 1 0 1 1
] - 34- 0 1 1 1 0 0
( - 35- 0 1 1 1 0 1
< - 36- 0 1 1 1 1 0 (= <)
\ - 37- 0 1 1 1 1 1
^ - 40- 1 0 0 0 0 0 (arrow ^)
J - 41- 1 0 0 0 0 1
K - 42- 1 0 0 0 1 0
L - 43- 1 0 0 0 1 1
M - 44- 1 0 0 1 0 0
N - 45- 1 0 0 1 0 1
O - 46- 1 0 0 1 1 0
P - 47- 1 0 0 1 1 1
Q - 50- 1 0 1 0 0 0
R - 51- 1 0 1 0 0 1
- - 52- 1 0 1 0 1 0
$ - 53- 1 0 1 0 1 1
* - 54- 1 0 1 1 0 0
) - 55- 1 0 1 1 0 1
; - 56- 1 0 1 1 1 0
' - 57- 1 0 1 1 1 1
` - 60- 1 1 0 0 0 0
/ - 61- 1 1 0 0 0 1
S - 62- 1 1 0 0 1 0
T - 63- 1 1 0 0 1 1
U - 64- 1 1 0 1 0 0
V - 65- 1 1 0 1 0 1
W - 66- 1 1 0 1 1 0
X - 67- 1 1 0 1 1 1
Y - 70- 1 1 1 0 0 0
Z - 71- 1 1 1 0 0 1
< - 72- 1 1 1 0 1 0 (arrow <)
, - 73- 1 1 1 0 1 1
% - 74- 1 1 1 1 0 0
= - 75- 1 1 1 1 0 1
" - 76- 1 1 1 1 1 0
! - 77- 1 1 1 1 1 1

Examples of BCD sixbit codes

CDC 1604 : Magnetic tape BCD codes

	.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.		1	2	3	4	5	6	7	8	9	0	#	@			tape mark
1.	space	/	S	T	U	V	W	X	Y	Z	record mark	,	%
2.	−	J	K	L	M	N	O	P	Q	R	−0	$	*
3.	&	A	B	C	D	E	F	G	H	I	+0	.	¤			group mark

CDC 1604 : Punched card codes

	.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.		1	2	3	4	5	6	7	8	9	0	=	−
1.	space	/	S	T	U	V	W	X	Y	Z		,	(
2.	---	J	K	L	M	N	O	P	Q	R	−0	$	*
3.	+	A	B	C	D	E	F	G	H	I	+0	.	)

CDC 1612 printer codes (business applications)

	.0	.1	.2	.3	.4	.5	.6	.7	.8	.9	.A	.B	.C	.D	.E	.F
0.	:	1	2	3	4	5	6	7	8	9	0	=	≠	≤	!	[
1.	space	/	S	T	U	V	W	X	Y	Z	]	,	(	→	≡	~
2.	−	J	K	L	M	N	O	P	Q	R	%	$	*	↑	↓	>
3.	+	A	B	C	D	E	F	G	H	I	<	.	)	≥	?	;

See also

• Binary-coded decimal
• Six-bit character code
• DEC Radix-50
• IBM Transcode
• ASCII
• Baudot code
• EBCDIC
• Unicode
• ANSI X3.64
• UTF-8
• UTF-16

Further reading

• BULL GCOS8 Manual
• Mackenzie, Charles E. (1980). Coded Character Sets, History and Development. Addison-Wesley. ISBN 0-201-14460-3.