All OPC Toolbox™ Data Access objects support properties that enable you to control characteristics of the object:
The opcda client object properties control aspects of the
connection to the OPC server, and event information obtained from the server. For
example, you can use the Timeout property to define how long to wait
for the server to respond to a request from the client.
The dagroup object properties control aspects of the collection
of items contained within that group, including all logging properties. For example, the
UpdateRate property defines how often the items in the group must
be checked for value changes, as well as the rate at which data will be sent from the
server during a logging session.
The daitem object properties control aspects of a single server
item. For example, you use the DataType property to define the data
type that the server must use to send values of that server item to the OPC Toolbox software.
For all three toolbox objects, you can use the same toolbox functions to
View a list of all the properties supported by the object, with their current values
View the value of a particular property
Get information about a property
Set the value of a property
To view all the properties of an OPC Toolbox Data Access object, with their current values, use the
get function.
If you do not specify a return value, the get function displays the
object properties in categories that group similar properties together. Use the display form
of the get function to view the value of all properties for the toolbox
object.
This example uses the get function to display a list of all the
properties of the OPC dagroup object grp.
get(grp)
General Settings:
DeadbandPercent = 0
GroupType = private
Item = []
Name = group1
Parent = [1x1 opcda]
Tag =
TimeBias = 0
Type = dagroup
UpdateRate = 0.5000
UserData = []
Callback Function Settings:
CancelAsyncFcn = @opccallback
DataChangeFcn = []
ReadAsyncFcn = @opccallback
RecordsAcquiredFcn = []
RecordsAcquiredFcnCount = 20
StartFcn = []
StopFcn = []
WriteAsyncFcn = @opccallback
Subscription and Logging Settings:
Active = on
LogFileName = opcdatalog.olf
Logging = off
LoggingMode = memory
LogToDiskMode = index
RecordsAcquired = 0
RecordsAvailable = 0
RecordsToAcquire = 120
Subscription = onTo view the value of a particular property of an OPC Toolbox Data Access object, use the get function, specifying the
name of the property as an argument. You can also access the value of the property as you
would a field in a MATLAB® structure.
This example uses the get function to retrieve the value of the
Subscription property for the dagroup object.
get(grp,'Subscription')ans = on
This example illustrates how to access the same property by referencing the object as if it were a MATLAB structure.
grp.Subscription
ans = on
To get information about a particular property, use thepropinfo or opchelp function.
The propinfo function returns a structure that contains information
about the property, such as its data type, default value, and a list of all possible values
if the property supports such a list. This example uses propinfo to get
information about the LoggingMode property.
propinfo(grp,'LoggingMode')ans =
Type: 'string'
Constraint: 'enum'
ConstraintValue: {'memory' 'disk' 'disk&memory'}
DefaultValue: 'memory'
ReadOnly: 'whileLogging'The opchelp function returns reference information about the
property with a complete description. This example uses opchelp to get
information about the LoggingMode property.
opchelp(grp,'LoggingMode')To set the value of a particular property of an OPC Toolbox Data Access object, use the set function, specifying the
name of the property as an argument. You can also assign the value to the property as you
would a field in a MATLAB structure.
Note
Because some properties are read-only, only a subset of the toolbox object properties
can be set. Use the property reference pages or the propinfo function to determine if a property is read-only.
This example uses the set function to set the value of the
LoggingMode property.
set(grp,'LoggingMode','disk&memory')
To verify the new value of the property, use the get function.
get(grp,'LoggingMode')ans = disk&memory
This example sets and views the value of a property by using dot-notation.
grp.LoggingMode = 'disk';
grp.LoggingModeans = disk
To view a list of all the properties of a toolbox object that can be set, use the
set function.
set(grp)
General Settings:
DeadbandPercent
Name
Tag
TimeBias
UpdateRate
UserData
Callback Function Settings:
CancelAsyncFcn: character vector -or- function handle -or- cell array
DataChangeFcn: character vector -or- function handle -or- cell array
ReadAsyncFcn: character vector -or- function handle -or- cell array
RecordsAcquiredFcn: character vector -or- function handle -or- cell array
RecordsAcquiredFcnCount
StartFcn: character vector -or- function handle -or- cell array
StopFcn: character vector -or- function handle -or- cell array
WriteAsyncFcn: character vector -or- function handle -or- cell array
Subscription and Logging Settings:
Active: [ {on} | off ]
LogFileName
LoggingMode: [ {memory} | disk | disk&memory ]
LogToDiskMode: [ {index} | append | overwrite ]
RecordsToAcquire
Subscription: [ {on} | off ]When using the set function to display a list of settable properties,
all properties that have a predefined set of acceptable values list those values after the
property. The default value is enclosed in curly braces ({}). For
example, from the display shown above, you can set the Subscription
property for a dagroup object to 'on' or
'off', with the default value being 'on'. You can
set the LogFileName property to any value.
Some OPC Toolbox Data Access object properties change their read-only status, depending on the state of an object (defined by another property of that object, or the parent of that object). The toolbox uses two special read-only modes:
'whileConnected': These properties cannot be changed while the
client is connected to the OPC server. For example, the client's Host property is read-only while connected.
'whileLogging': These properties cannot be changed while the
dagroup object is logging. For example, the LoggingMode property is read-only while logging. For more information on
logging, see Log OPC Server Data.
'whilePublic': These properties cannot be changed because the
group is a public group. For more information on public groups, see Work with Public Groups.
Note
Properties that modify their read-only state are always displayed when using
set to display settable properties, even when they cannot be
changed because of the state of the object.
To determine if a property has a modifiable read-only state, use the propinfo function.