Allen-Bradley PLC-5 MAP/OSI, User Manual, Page: 13 / 135

Chapter 1
Overview of the MAP Communication
Environment
1-5
Definition). For a complete listing of the MMS services supported by your
OSI coprocessor, refer to Chapter 3 of this manual.
The dominant aspect of MMS is the concept of modeling. MMS defines
models that describe the way in which resources are made available and
the way in which these resources are accessed. At the center of the MMS
modeling concept are:
the Virtual Manufacturing Device (VMD)
abstract object models
The VMD
The VMD describes the externally visible behavior of an MMS device
when it makes resources (i.e., data table memory, program files) available
to other MMS devices. Assume, for example, that an MMS device exists
and it makes system data table memory available to other MMS devices. It
is the VMD that describes the way in which that MMS device makes the
data table memory available (figure 1.6).
Figure 1.6
The VMD Describes the Way a Device Makes its Resources Available
OSI Network
VMD
data table memory
The way this MMS device makes its
resources available is described by the
VMD.
This MMS device has requested
information on data table memory
from another device.
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It is each vendor’s responsibility to associate the VMD model with their
device (figure 1.7).
The MMS Modeling Concept
AB Parts