Chapter 3
Developing Your Application
3-10
ni.com
Step 4. Stop Communication
Before you exit your application, stop communication to shut down
DeviceNet connections to remote devices. Use the Interface Object to
call the
ncOperateDnetIntf
function with the
Opcode
parameter set
to
Stop
.
Step 5. Close Objects
Before you exit your application, close all NI-DNET objects using the
ncCloseObject
function.
Multiple Applications on the Same Interface
The NI-DNET software allows multiple NI-DNET applications to use the
same interface object simultaneously, as long as the interface configuration
remains the same. For example, you can run both the
SingleDevice
example and
SimpleWho
on
DNET0
as long as the
Interface MacId
,
BaudRate
, and
PollMode
parameters are the same in both applications
(
SimpleWho
uses a
PollMode
of
Scanned
). Similarly, you can open up
two copies of the
SingleDevice
example and communicate with two
different devices as if it were through a single application. These same rules
apply to the I/O Object and the Explicit Messaging Object.
As long as all the configuration attributes are the same, any object can be
opened multiple times. You can enable only one notification or wait
(through
ncWaitForState
,
ncCreateNotification
, or
ncCreateOccurrence
functions) for an object, no matter how many
handles you have opened for that particular object. For example, if you are
running two copies of the
SingleDevice
example on the same interface
with the same connection types, the notification triggers in only one
application at a time.
The synchronization of events and the protection of the object I/O data is
the responsibility of the application developer. Similarly, the application
performance might change based on the number of objects open and the
frequency of API calls made in each application. For example, several calls
to
ncGetDnetAttribute
in one application might slow down another
application running on the same interface.
To ensure proper clean up of all the objects, each open call to an object
should be matched by a close call to the same object, and each call to
ncOperateDnetIntf
with
NC_OP_START
code should be matched by
a call to the same function with
NC_OP_STOP
code.
