6100 ADCCP Programming Manual

6100 ADCCP Concepts and Context
Introduction to 6100 ADCCP
1–6 069225 Tandem Computers Incorporated
A link that connects only two devices is called a point-to-point link; a link that
connects more than two devices is called a multipoint link. (The primary station on a
multipoint link is sometimes referred to as a supervisor, and the secondary stations
are sometimes referred to as tributaries. This manual uses the terms primary and
secondary only.) Links between combined stations are always point-to-point.
Line-Control Modes The line-control mode determines the commands a primary station or substation
issues to enable data transmission. The line-control mode also determines how a
secondary station or substation responds to a primary station. ADCCP defines three
modes plus an extended mode for each of the three modes. The three modes are:
Normal Response Mode (NRM)
Asynchronous Response Mode (ARM)
Asynchronous Balanced Mode (ABM)
Normal Response Mode (NRM)
In NRM , a secondary station may transmit data only after a request from the primary
station. On a point-to-point line, the primary station polls the secondary station; on a
multipoint line, the primary station polls the secondaries in a round-robin sequence.
(See Section 2, “ADCCP Link and Station Management,” for a more detailed
description of multipoint polling.) Figure 1-2 shows NRM.
In figure 1-2, the primary station issues a SNRM to set up the line. The secondary
station responds with a UA. The primary stations polls the secondary station for data:
RR(P). The secondary station responds with information frames.
Figure 1-2. NRM Line-Control Mode
Link Management (Example) Data Transfer
Primary Station
Secondary
Station
SNRM
UA
Primary Station
Secondary
Station
RR(P)
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