Transcode (character encoding)

IBM Six-Bit Transcode

Company type	Character encoding
Industry	Computer hardware, telecommunications
Founded	1967
Products	Six-bit character set for data transmission
Parent	IBM

Six-Bit Transcode, also known as Six-Bit Transmission Code, was among the trio of character sets IBM utilized for Binary Synchronous Communications during a specific timeframe. This encoding enabled faster data transfer compared to 8-bit EBCDIC or ASCII when the information was confined to a limited set of 48 characters.

The IBM 2780 data transmission terminal, which debuted in 1967, incorporated support for Transcode. However, its follow-up model, the IBM 3780 terminal released in 1972, removed Transcode compatibility and introduced a "space compression" capability instead.

Transcode represents a six-bit character code connected to IBM's punched card code, yet unlike EBCDIC, it is not a form of BCD. It encompasses 64 distinct codes: 26 uppercase alphabetic characters, 10 numeric digits, 11 special symbols, the space character, and 16 control characters. The set of 48 printable characters includes ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 .'-/@#$%&*⌑ while excluding ,:;!?"()[]<>+^=_\`{}|~. Transmission employs odd parity for each character. In Transcode mode on the 2780 terminal, the 16 control characters are not permitted as data.

Code table

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Code table (from 2780 manual)

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Character	Punched card code	6-bit transcode	Hex
SOH	12-9-1	P	00
A	12-1	5	01
B	12-2	4	02
C	12-3	4 5 P	03
D	12-4	3	04
E	12-5	3   5 P	05
F	12-6	3 4   P	06
G	12-7	& nbsp; & nbsp;3 4 5  & nbsp;	07
H	12-8	& nbsp;2 & nbsp; & nbsp; & nbsp; & nbsp; & nbsp;	08
I	12-9	& nbsp;2 & nbsp;	09
STX	12-9-2	& nbsp;2 & nbsp;;4 ;; P	0A
.	12-8-3	& nbsp;;2 ;;4 ;;5 ;;	0B
⌑	12-8-4	& nbsp;;2 ;;3 ;; P	0C
BEL	0-9-8-7	& nbsp;;2 ;;3 ;;5 ;;	0D
Sub	9-8-7	& nbsp;;2 ;;3 ;;4 ;;	0E
ETB	0-9-6	& nbsp;;2 ;;3 ;;4 ;;5 ;; P	0F
& &​​​​​​​​​​​​​​​​​​​​​​​​​​​	10
11-1 |1 |5 |P |11
11-2 |1 |4 | |P |12
11-3 |1 |4 |5 | |13
11-4 |1 |3 | |P |14
11-5 |1 |3 |5 | |15
11-6 |1 |3 |4 | |16
11-7 |1 |3 |4 |5 |P |17
11-8 |1 |2 | |P |18
11-9 |1 |2 |5 |	19
Space	no punch	1  2  4	1A
$	11-8-3	1  2   4  5   P	1B
*	11-8-4	1   2   3

Devices Employing Transcode

• IBM 2701 Data Adapter Unit
• IBM 2703 Transmission Controller
• IBM 2780 Data Transmission Terminal
• IBM System/370 model 135 Integrated Communications Adapter (ICA)