Transcode (character encoding)

Six-Bit Transcode, or Six-Bit Transmission Code, was, for a few years, one of the three character sets used by IBM for Binary Synchronous Communications. Transmission using 6-bit Transcode had higher throughput than transmission using 8-bit EBCDIC or ASCII, provided that the data to be transmitted used a limited set of 48 characters.

For other uses, see Transcode (disambiguation).

The IBM 2780 data transmission terminal was announced with Transcode support in 1967. Its successor, the IBM 3780 data communication terminal, announced in 1972, dropped Transcode support and added a "space compression" option.

Transcode is a six-bit character code. It relates to IBM's punched card code but, like EBCDIC, it is not BCD. Its 64 values consist of the 26 uppercase letters, 10 numbers, 11 symbols, space, and 16 control characters. Its 48 printable characters are ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 .'-/@#$%&*⌑; it cannot represent ,:;!?"()[]<>+^=_\`{}|~. Characters are transmitted with odd parity. The 2780 cannot use the 16 control characters as data characters in Transcode mode.[1]

Code table
Six-Bit Transcode
0 1 2 3 4 5 6 7 8 9 A B C D E F
0x SOH A B C D E F G H I STX . ⌑ BEL SUB ETB
1x & J K L M N O P Q R SP $ * IUS/
ITB		 EOT DLE
2x - / S T U V W X Y Z ESC ' % ENQ ETX HT
3x 0 1 2 3 4 5 6 7 8 9 SYN # @ NAK EM DEL

Code table (from 2780 manual)
Character
 		Punched card
code		6-bit
transcode		Hex 
SOH12-9-1             P00
A12-1           5  01
B12-2         4    02
C12-3         4 5 P03
D12-4       3      04
E12-5       3   5 P05
F12-6       3 4   P06
G12-7       3 4 5  07
H12-8     2        08
I12-9     2     5 P09
STX12-9-2     2   4   P0A
.12-8-3     2   4 5  0B
⌑12-8-4     2 3     P0C
BEL0-9-8-7     2 3   5  0D
Sub9-8-7     2 3 4    0E
ETB0-9-6     2 3 4 5 P0F
&12   1          10
J11-1   1       5 P11
K11-2   1     4   P12
L11-3   1     4 5  13
M11-4   1   3     P14
N11-5   1   3   5  15
O11-6   1   3 4    16
P11-7   1   3 4 5 P17
Q11-8   1 2       P18
R11-9   1 2     5  19
Spaceno punch   1 2   4    1A
$11-8-3   1 2   4 5 P1B
*11-8-4   1 2 3      1C
US11-9-8-7   1 2 3   5 P1D
EOT9-7   1 2 3 4   P1E
DLE12-11-9-8-1   1 2 3 4 5  1F
-11 0            20
/0-1 0         5 P21
S0-2 0       4   P22
T0-3 0       4 5  23
U0-4 0     3     P24
V0-5 0     3   5  25
W0-6 0     3 4    26
X0-7 0     3 4 5 P27
Y0-8 0   2       P28
Z0-9 0   2     5  29
ESC0-9-7 0   2   4    2A
'0-8-3 0   2   4 5 P2B
 %0-8-4 0   2 3      2C
ENQ0-9-8-5 0   2 3   5 P2D
ETX12-9-3 0   2 3 4   P2E
HT12-9-5 0   2 3 4 5  2F
00 0 1         P30
11 0 1       5  31
22 0 1     4    32
33 0 1     4 5 P33
44 0 1   3      34
55 0 1   3   5 P35
66 0 1   3 4   P36
77 0 1   3 4 5  37
88 0 1 2        38
99 0 1 2     5 P39
SYN9-2 0 1 2   4   P3A
#8-3 0 1 2   4 5  3B
@8-4 0 1 2 3     P3C
NAK9-8-5 0 1 2 3   5  3D
EM11-9-8-1 0 1 2 3 4    3E
DEL12-9-7 0 1 2 3 4 5 P3F

Devices using Transcode

References
  1. IBM Corporation (1971). Component Description: IBM 2780 Communications Terminal (PDF). Archived (PDF) from the original on 2020-07-26.
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