Synchronous transmit-receive

Synchronous transmit-receive (STR) was an early IBM communications protocol which preceded Bisync. STR was point-to-point only, and employed a four-of-eight transmission code, communicating at up to 5100 characters per second over half-duplex or full-duplex communication lines.

The IBM 1130 Synchronous Communications Adapter, the IBM System/360 model 20 Communications Adapter, and the IBM 2701 Data Transmission Unit provided host computer support for STR.

The IBM 1009 Data Transmission Unit, the IBM 7701, the IBM 7702 Magnetic Tape Transmission Terminal, the IBM 1013 Card Transmission Terminal, and the IBM 7710 and IBM 7711 Data Communication Units were among the remote devices supported by STR.^[1]

STR was still supported as of 1972,^[1] although it had generally faded from use.

Four-of-eight code

The four-of-eight code was a 64 character set plus seven control characters, encoded in eight bits. Exactly four bits of each character were one bits.

Data codes

This is the four-of-eight code for the IBM 1130 Synchronous Communications Adapter (SCA):

Graphic	four-of-eight code	Hex
	N X O R 8 4 2 1
blank¹	1 1 1 1 0 0 0 0	F0
¢	0 1 1 0 1 0 1 0	6A
.	1 0 0 0 1 0 1 1	8B
<	0 1 1 0 1 1 0 0	6C
(	0 1 0 1 0 1 1 0	56
+	0 0 1 1 0 1 1 0	36
\|²	1 0 0 0 1 1 0 1	8B
&	1 0 0 0 1 1 1 0	8E
!	1 1 0 0 1 0 1 0	CA
$	0 1 0 0 1 0 1 1	4B
*	1 1 0 0 1 1 0 0	CC
)	0 1 0 1 1 1 0 0	5C
;	0 0 1 1 1 1 0 0	3C
¬	0 1 0 0 1 1 0 1	4D
-	0 1 0 0 1 1 1 0	4E
/	1 0 1 1 0 0 0 1	B1
,	0 0 1 0 1 0 1 1	2B
%	1 0 1 0 1 1 0 0	AC
_	0 1 0 1 1 0 1 0	5A
>	0 0 1 1 1 0 1 0	3A
?	0 0 1 0 1 1 0 0	2D
:¹	0 0 1 1 1 1 0 0	2E
#	0 0 0 1 1 0 1 1	1B
@	1 0 0 1 1 1 0 0	9C
'	0 0 0 0 1 1 1 1	0F
=	0 0 0 1 1 1 1 0	1E
"	0 0 0 1 1 1 0 1	1D
A	0 1 1 1 0 0 0 1	71
B	0 1 1 1 0 0 1 0	72
C	0 1 1 0 0 0 1 1	63
D	0 1 1 1 0 1 0 0	74
E	0 1 1 0 0 1 0 1	65
F	0 1 1 0 0 1 1 0	66
G	1 0 0 0 0 1 1 1	87
H	0 1 1 1 1 0 0 0	78
I	0 1 1 0 1 0 0 1	69
J	1 1 0 1 0 0 0 1	D1
K	1 1 0 1 0 0 1 0	D2
L	1 1 0 0 0 0 1 1	C3
M	1 1 0 1 0 1 0 0	D4
N	1 1 0 0 0 1 0 1	C5
O	1 1 0 0 0 1 1 0	C6
P	0 1 0 0 0 1 1 1	47
Q	1 1 0 1 1 0 0 0	D8
R	1 1 0 0 1 0 0 1	C9
(none)³	1 0 1 0 1 0 1 0	AA
S	1 0 1 1 0 0 1 0	B2
T	1 0 1 0 0 0 1 1	A3
U	1 0 1 1 0 1 0 0	B4
V	1 0 1 0 0 1 0 1	A5
W	1 0 1 0 0 1 1 0	A6
X	0 0 1 0 0 1 1 1	27
Y	1 0 1 1 1 0 0 0	B8
Z	1 0 1 0 1 0 0 1	A9
0	1 0 0 1 1 0 1 0	9A
1	1 1 1 0 0 0 0 1	E1
2	1 1 1 0 0 0 1 0	E2
3	1 0 0 1 0 0 1 1	93
4	1 1 1 0 0 1 0 0	E4
5	1 0 0 1 0 1 0 1	95
6	1 0 0 1 0 1 1 0	96
7	0 0 0 1 0 1 1 1	17
8	1 1 1 0 1 0 0 0	E8
9	1 0 0 1 1 0 0 1	99
	¹model-dependent ²Group Mark ³Record Mark

Control codes

Synchronous transmit-receive control codes:

Graphic	four-of-eight code	Hex
	N X O R 8 4 2 1
Idle	0 0 1 1 1 0 0 1	39
Start of Record 1 or acknowledge 1 (SOR 1 or ACK 1)	0 1 0 1 0 0 1 1	53
start of record 2 or acknowledge 2 (SOR 2 or ACK2 )	0 0 1 1 0 0 1 1	33
Transmit Leader (TL)	0 0 1 1 0 1 0 1	35
Control Leader (CL)	0 1 0 1 0 1 0 1	55
End of Transmission (EOT)¹	0 1 0 1 1 0 1 0	5A
Inquiry or Error (INQ or ERR)	0 1 0 1 1 0 0 1	59
Telephone¹	0 1 0 1 1 1 0 0	5C
Group Mark	1 0 0 0 1 1 0 1	8D
Longitudinal Redundancy Check (LRS)	- - - - - - - -
¹also used as a data character

References

^ ^a ^b IBM Corporation (1972). IBM 1130 Functional Characteristics (PDF). pp. 171–172.

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[FC1130-1] IBM Corporation (1972). IBM 1130 Functional Characteristics (PDF). pp. 171–172.

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