User manual

Computer Gateway User Manual 5-1 5/96

DATA LINK CHARACTERISTICS

Section 5

This section summarizes the data link hardware, transaction management, and supported

protocols (Bisynch and HDLC). See Appendix B for cabling and connector information.

5.1 INTRODUCTION

Communication between the host processor and the CG is over a serial link, using either

Binary Synchronous (Bisynch) or HDLC protocol. When Bisynch is used, either one or

two half-duplex links can be used (one is recommended). When HDLC is used, one full-

duplex link is supported. You are expected to provide a compatible data link package for

your host processor.

5.2 HARDWARE INTERFACES

The following hardware interfaces are supported:

RS232C EIA Standard RS232C connectors are used. Cable lengths greater than 50

feet require a modem. Speeds are: 1200, 1760, 2152, 2400, 4800, 9600, or

19200 baud.

RS422 RS449 37-pin connectors are used. For cable lengths up to 4000 feet. Full

duplex channels are supported. Speeds are 1200, 1760, 2152, 2400, 4800,

9600, 19200, 38400, 57600 (HDLC limit), and 76800 baud.

Circuits used:

• Shield (connected to the CG end only)

• Signal Ground (circuit SG)

• Send Data (circuit SD)

• Receive Data (circuit RD)

• Data Mode (circuit DM)

• Terminal Ready (circuit TR)

5.3 BISYNCH PROTOCOL

Binary Synchronous Communication Protocol Procedure for Point-to-Point Operation with

Contention, as described in the IBM publication GA27-3004-2, General Information—

Binary Synchronous Communications, is provided.

This implementation uses transparent Bisynch with EBCDIC-control characters (see Table

5-1 for hexadecimal equivalents for the EBCDIC-control characters). The maximum

transmission block size is 512 words (1024 bytes). Both single- and multiple-block

transactions are supported (13 block maximum). The Bisynch header is not used, instead a

message-specific header is included as part of the ASCII character-text message in each

block. See Section 4 for details of the individual message formats.