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Chapter 3
MMS and Your Coprocessor
3-5
MMS Service: Support: Description:
DefineNamed
Variable
This is used by the PLC-5 system, in conjunction with the OSI coprocessor,
to define an MMS named variable. An MMS client can also use this to define
a named variable within the coprocessor. The named variable would
reference a location within the PLC-5 system.
Client and server. The client side of the DefineNamedVariable
service within the OSI coprocessor is invoked by programming
a DEFVAR command within a PLC-5 system message
instruction. The server side is invoked when the OSI
coprocessor receives a DefineNamedVariable request. The
server side does not support domain-specific named variables.
DeleteVariable
Access
This is used by the PLC-5 system in conjunction with the OSI coprocessor to
delete an MMS named variable. An MMS client uses this to delete a named
variable within the OSI coprocessor. Note that when this service is directed to
an OSI coporcessor, no PLC-5 system memory is deleted, only the named
variable reference within the interface is deleted.
Client and server. The client side of the DeleteVariableAccess
service within the OSI coprocessor is invoked by programming
a DELVAR command within a PLC-5 system message
instruction. The server side is invoked when the OSI
coprocessor receives a DeleteVariableAccess request.
DefineNamed
VariableList
An MMS client uses this to define an identifier string that references a list of
variable objects. Thus, by specifying a single name in a read or write request,
the client could access multiple, possibly discontiguous, PLC-5 controller
memory locations.
Server. The server side of the DefineNamedVariableList
service is invoked when the OSI coprocessor receives a
DefineNamedVariableList request. The server side does not
support domain-specific named variable lists.
GetNamedVariable
ListAttributes
An MMS client uses this to obtain a list of the variable objects that are
members of the named variable list.
Server. The server side of the GetNamedVariableListAttributes
service is invoked when the OSI coprocessor receives a
GetNamedVariableListAttributes request.
DeleteNamed
VariableList
An MMS client uses this to delete a previously defined named variable list.
Note that this does not delete any memory within the PLC-5 system. It only
removes the named variable list object from the OSI coprocessor.
Server. The server side of the DeleteNamedVariableList
service is invoked when the OSI coprocessor receives a
DeleteNamedVariableList request.
DefineNamedType An MMS client uses this service to define a ``data type template" to be used at
a later time when either accessing memory within the PLC-5 system (using
the read and/or write service) or when defining named variables (using the
DefineNamedVariable service within the OSI coprocessor).
Server. The server side of the DefineNamedType service is
invoked when the OSI coprocessor receives a
DefineNamedType request.The server side does not support
domain-specific named types.
GetNamedType
Attributes
An MMS client uses this service to obtain the characteristics associated with
a previously defined named type within the OSI coprocessor. When the OSI
coprocessor receives this request, it returns the ``data type template" that was
previously defined.
Server. The server side of the GetNamedTypeAttributes
service is invoked when the OSI coprocessor receives a
GetNamedTypeAttributes request.
DeleteNamedType An MMS client uses this service to remove a previously defined named type
from the OSI coprocessor.
Server. The server side of the DeleteNamedType service is
invoked when the OSI coprocessor receives a
DeleteNamedType request.
Additional Information Regarding MMS Services
All addresses must be in MMS ‘‘Symbolic Address” format
VMD–specific and Application Association–specific named variables, named variable lists, and named
types are supported. Domain–specific named variables, named variable lists, and named types are not
supported.
There is no fixed limit for the number of variables in a ‘‘list of variables” for the variable access services.
The number is limited only due to negotiated PDU size and available memory within the coprocessor.
The list of capabilities is always reported as NULL in GetDomainAttributes and you must specify as NULL
in InitiateDownloadSequence.
The maximum PDU size supported is 1800 octets.
AB Parts