PREFACE
This manual is written as a reference text and is intended to cover all the major facets of the IBM 270:1 from a hardwarc \'iewpoint. Further informa­
tion pertaining specifically to the IB:\I System/360 is contained in the 113),1 Principles of Operation manual, Form GA22-6821. Numerous pro­
gramming publications describing the various tele­
communications programs are also available. All
these publications are listed in the IBM System/360 Form GA22-6822. Third Edition (Septenlber 1970) This is a reprint of the Second Edition, incorporating changes released in the following
Technical Newsletters:
N27 - 3027 (date d June 1968)
N27 - 3029 (dated December 1968) 1\27-3038 (dated April 1969) 1'.,'27-3043 (dated July 1969) (dated February 9, 107()\ .J..,../f VJ
Changes are periodically made to the information herein; before using this publication
in connection with the operation of IB\1 systems or equipment, refer to the latest SRL Nevv·sletter for the editions that are applicable and current.
Requests for copies of IB\i publication, should be made to your IB\f representative or to
the IB-'l branch offi ce serving your locality.
This manual bas been prepared by tbe IB\l Systems Development Division, Publications Center, Department lOI, P. 0, Box 12275, Research Triangle Park, North Carolina ;\ forn1 for reader's comrnents is provjded at the back of this publication. If
the form has been removed, comments may be sent to the above address. I

INTRODUCTION • General Description of Operations
DETAILED DESCRIPTION OF OPERATIONS CommWlications-line Addressing
Operation with the Multiplexer Channel • Programming Considerations Special Features Summary • START/STOP COMMUNICATIONS CAPABIliTIES • line Control
Transmit Operation (Write Command)
Receive Operation (Read Command).
Commands
Status-Byte Conditions • Sense-Byte Conditions • Start/Stop Special Features.
Terminal Control Operations
Figure
1. IBM 2703 Transmission Control • 2. Data Communications Units Attachable to the 2703 .
3. 2703-Internal Organization
4. Main Control Words (MCW-1, MCW-2) and Main
Data Words (MDW-1, MDW-2)
5. Bit Configuration of a "G" Character (Serialized)
6. line-Control Characters
7. Start/ Stop Commands • 8. Line Base Configurations.
9. Typical 2712 Configuration
5
7
11
12
14
15
19
23
23
24
24
25
28
30
35
39 Page • iv
6 • 8 • 17 • 23 • 23 • 26 • 37 • 39 CONTENTS BSC (BINARY SYNCHRONOUS COMMUNICATIONS) CAPA­ BIliTIES
Introduction to BSC General Description of BSC Operations Synchronous Operations
Binary Synchronous Commands • Fifect of Halt I/O Instruction and Zero Byte Count. APPENDIX A. OPERA TOR'S CONTROL PANEL Indicators Switches Metering APPENDIX B. COMMUNICATIONS FACIliTIES
Common-Carrier-Provided Facilities.
Privately Owned Commtmications Facilities
INDEX • 47 • 47 • 47 50 55
62
65 • 65
65
65
68
68
69
71 ILLUSTRATIONS Figure
10. Total Low-Speed lines Available by 2712 Model
Configurations
11. Operation of Two System/360 Computers over a
Communications line • 12. Code Translation of a Received Character (to
EBCDIC or ASCII-8) 13. Communications Facilities for BSC 14. MultipOint Configuration
15. Transparent Operation • 16. Operator's Panel • Page .40
.52 • 52
.55
.56
.60
.66
iii