Allen-Bradley PLC-5 MAP/OSI, Руководство пользователя, Страница: 16 / 135

Chapter 1
Overview of the MAP Communication
Environment
1-8
merely a grouping of domains within a system. Therefore, within the OSI
coprocessor, the single program invocation object is made up of a single
domain object.
Variable Objects Implemented by the OSI Coprocessor
Your OSI coprocessor implements the following types of variable objects:
Variable Object: Description:
Named Variables MMS allows you to associate a name with an address within the node
(i.e., `paint_station' for address N12:1). The names are identification
strings. To gain access to the address, simply specify the name.
Unnamed Variables (or
address strings)
Variables that do not have an identifier string associated with an
address. To access the location, you must specify the address.
Named Variable Lists This is a grouping of named and/or unnamed variables referenced by
a single identification string.
Named Types These are objects that pre-define a data-type template for use when
accessing unnamed variables or defining named variables. For
example, if a client has defined a template for an array of 100 integers
called 'int_array_100' within the OSI coprocessor, and the client sends
a read request for ``N7:0", specifying 'int_array_100' as the data type
to be returned, the client will receive an array of 100 integers starting
at ``N7:0".
Clients, Servers, and MMS Modeling
In the previous sections we covered the various concepts of MMS
modeling. It is important to note here that the MMS specification defines
models for the behavior of a device acting as a server, but not as a client.
Within the MMS specification, the terms client and server are used to
describe the tasks that a device performs when it carries out an MMS
service. An MMS device that makes resources available for use by another
MMS device is called a server. And the MMS device that makes use of
those resources to perform some type of application function is called a
client (figure 1.9).