BS 6556-3:1985

Foreword
Committees responsible
Specification
0 Introduction
1 Scope
2 Definitions and abbreviations
3 Link configurations
4 Transmissions
5 Checks
6 Data only protocol (DOP)
7 Simple asynchronous protocol (SAP)
8 Marking
Appendix
A Method for the generation and verification of check
    field (CF)
Tables
1 Start of message (SMB) codes
2 Valid address bytes
3 Stuffing codes
Figures
1 The components of the byte transmission
2 Operation using DOP
3 Operation for 1 to 15 slaves using SAP
4 Application data message (ADM) and broadcast message
    (BRO) format
5 Link control message (LCM) and initialization
    message (IM) format
6 A 2 byte transmission
7 Transmission envelope from slave with modem
8 Slave response to poll (current loop link)
9 Slave response to poll (MODEM link)
10 Composition of message address byte (AB)
11 Composition of application data description byte
    (ADD)

Specifies the message protocols employed with intrinsicaly safe transmitting and receiving circuits forming low speed digital data transmission links in which the data is transmitted by optical or transformer couplings.

This Part of BS 6556 specifies two message protocols employed with particular low speed digital signals systems for use in coal mines, using either optical coupling (see BS 6556-1) or transformer coupling (see BS 6556-2). Either protocol can be employed in either transmission system.

The protocols require only limited station intelligence for successful implementation. One protocol, known as simple asynchronous protocol, is designed to work in point-to-point or multi-drop configurations. The other protocol, known as data only protocol, will only work in point-to-point configurations.

Protocol for the applications data is not specified by this standard although industry standards will exist to regulate this.

NOTE The titles of the publications referred to in this standard are listed on the inside back cover.